{-# LANGUAGE BangPatterns               #-}
{-# LANGUAGE CPP                        #-}
{-# LANGUAGE DeriveDataTypeable         #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module Agda.TypeChecking.Monad.Base where

import Prelude hiding (null)

import qualified Control.Concurrent as C
import qualified Control.Exception as E

#if __GLASGOW_HASKELL__ >= 800
import qualified Control.Monad.Fail as Fail
#endif

import Control.Monad.State
import Control.Monad.Reader
import Control.Monad.Writer hiding ((<>))
import Control.Monad.Trans.Maybe
import Control.Applicative hiding (empty)

import Data.Function
import Data.Int
import Data.IntMap (IntMap)
import qualified Data.IntMap as IntMap
import qualified Data.List as List
import Data.Maybe
import Data.Map (Map)
import qualified Data.Map as Map -- hiding (singleton, null, empty)
import Data.Monoid ( Monoid, mempty, mappend )
import Data.Sequence (Seq)
import Data.Set (Set)
import qualified Data.Set as Set -- hiding (singleton, null, empty)
import Data.Semigroup ( Semigroup, (<>), Any(..) )
import Data.Data (Data, toConstr)
import Data.Foldable (Foldable)
import Data.String
import Data.Text.Lazy (Text)
import qualified Data.Text.Lazy as T
import Data.Traversable
import Data.IORef

import qualified System.Console.Haskeline as Haskeline

import Agda.Benchmarking (Benchmark, Phase)

import Agda.Syntax.Concrete (TopLevelModuleName)
import Agda.Syntax.Common
import qualified Agda.Syntax.Concrete as C
import Agda.Syntax.Concrete.Definitions
  (NiceDeclaration, DeclarationWarning, declarationWarningName)
import qualified Agda.Syntax.Abstract as A
import Agda.Syntax.Abstract (AllNames)
import Agda.Syntax.Internal as I
import Agda.Syntax.Internal.Pattern ()
import Agda.Syntax.Internal.Generic (TermLike(..))
import Agda.Syntax.Literal
import Agda.Syntax.Parser (PM(..), ParseWarning, runPMIO)
import Agda.Syntax.Parser.Monad (parseWarningName)
import Agda.Syntax.Treeless (Compiled)
import Agda.Syntax.Fixity
import Agda.Syntax.Position
import Agda.Syntax.Scope.Base
import qualified Agda.Syntax.Info as Info

import Agda.TypeChecking.CompiledClause
import Agda.TypeChecking.Coverage.SplitTree
import Agda.TypeChecking.Positivity.Occurrence
import Agda.TypeChecking.Free.Lazy (Free(freeVars'), bind', bind)

import Agda.Termination.CutOff

import {-# SOURCE #-} Agda.Compiler.Backend

-- import {-# SOURCE #-} Agda.Interaction.FindFile
import Agda.Interaction.Options
import Agda.Interaction.Options.Warnings
import Agda.Interaction.Response
  (InteractionOutputCallback, defaultInteractionOutputCallback, Response(..))
import Agda.Interaction.Highlighting.Precise
  (CompressedFile, HighlightingInfo)
import Agda.Interaction.Library

import Agda.Utils.Except
  ( Error(strMsg)
  , ExceptT
  , MonadError(catchError, throwError)
  , runExceptT
  , mapExceptT
  )

import Agda.Utils.Benchmark (MonadBench(..))
import Agda.Utils.FileName
import Agda.Utils.HashMap (HashMap)
import qualified Agda.Utils.HashMap as HMap
import Agda.Utils.Hash
import Agda.Utils.Lens
import Agda.Utils.List
import Agda.Utils.ListT
import Agda.Utils.Monad
import Agda.Utils.NonemptyList
import Agda.Utils.Null
import Agda.Utils.Permutation
import Agda.Utils.Pretty hiding ((<>))
import qualified Agda.Utils.Pretty as P
import Agda.Utils.Singleton
import Agda.Utils.Functor
import Agda.Utils.Function
import Agda.Utils.WithDefault ( collapseDefault )

#include "undefined.h"
import Agda.Utils.Impossible

---------------------------------------------------------------------------
-- * Type checking state
---------------------------------------------------------------------------

data TCState = TCSt
  { stPreScopeState   :: !PreScopeState
    -- ^ The state which is frozen after scope checking.
  , stPostScopeState  :: !PostScopeState
    -- ^ The state which is modified after scope checking.
  , stPersistentState :: !PersistentTCState
    -- ^ State which is forever, like a diamond.
  }

class Monad m => ReadTCState m where
  getTCState :: m TCState
  withTCState :: (TCState -> TCState) -> m a -> m a

instance ReadTCState m => ReadTCState (MaybeT m) where
  getTCState = lift getTCState
  withTCState = mapMaybeT . withTCState

instance ReadTCState m => ReadTCState (ListT m) where
  getTCState = lift getTCState
  withTCState f = ListT . withTCState f . runListT

instance ReadTCState m => ReadTCState (ExceptT err m) where
  getTCState = lift getTCState
  withTCState = mapExceptT . withTCState

instance ReadTCState m => ReadTCState (ReaderT r m) where
  getTCState = lift getTCState
  withTCState = mapReaderT . withTCState

instance (Monoid w, ReadTCState m) => ReadTCState (WriterT w m) where
  getTCState = lift getTCState
  withTCState = mapWriterT . withTCState

instance ReadTCState m => ReadTCState (StateT s m) where
  getTCState = lift getTCState
  withTCState = mapStateT . withTCState

instance Show TCState where
  show _ = "TCSt{}"

data PreScopeState = PreScopeState
  { stPreTokens             :: !CompressedFile -- from lexer
    -- ^ Highlighting info for tokens (but not those tokens for
    -- which highlighting exists in 'stSyntaxInfo').
  , stPreImports            :: !Signature  -- XX populated by scopec hecker
    -- ^ Imported declared identifiers.
    --   Those most not be serialized!
  , stPreImportedModules    :: !(Set ModuleName)  -- imports logic
  , stPreModuleToSource     :: !ModuleToSource   -- imports
  , stPreVisitedModules     :: !VisitedModules   -- imports
  , stPreScope              :: !ScopeInfo
    -- generated by scope checker, current file: which modules you have, public definitions, current file, maps concrete names to abstract names.
  , stPrePatternSyns        :: !A.PatternSynDefns
    -- ^ Pattern synonyms of the current file.  Serialized.
  , stPrePatternSynImports  :: !A.PatternSynDefns
    -- ^ Imported pattern synonyms.  Must not be serialized!
  , stPreGeneralizedVars    :: !(Maybe (Set QName))
    -- ^ Collected generalizable variables; used during scope checking of terms
  , stPrePragmaOptions      :: !PragmaOptions
    -- ^ Options applying to the current file. @OPTIONS@
    -- pragmas only affect this field.
  , stPreImportedBuiltins   :: !(BuiltinThings PrimFun)
  , stPreImportedDisplayForms :: !DisplayForms
    -- ^ Display forms added by someone else to imported identifiers
  , stPreImportedInstanceDefs :: !InstanceTable
  , stPreForeignCode        :: !(Map BackendName [ForeignCode])
    -- ^ @{-\# FOREIGN \#-}@ code that should be included in the compiled output.
    -- Does not include code for imported modules.
  , stPreFreshInteractionId :: !InteractionId
  , stPreImportedUserWarnings :: !(Map A.QName String)
    -- ^ Imported @UserWarning@s, not to be stored in the @Interface@
  , stPreLocalUserWarnings    :: !(Map A.QName String)
    -- ^ Locally defined @UserWarning@s, to be stored in the @Interface@
  }

type DisambiguatedNames = IntMap A.QName

data PostScopeState = PostScopeState
  { stPostSyntaxInfo          :: !CompressedFile
    -- ^ Highlighting info.
  , stPostDisambiguatedNames  :: !DisambiguatedNames
    -- ^ Disambiguation carried out by the type checker.
    --   Maps position of first name character to disambiguated @'A.QName'@
    --   for each @'A.AmbiguousQName'@ already passed by the type checker.
  , stPostMetaStore           :: !MetaStore
  , stPostInteractionPoints   :: !InteractionPoints -- scope checker first
  , stPostAwakeConstraints    :: !Constraints
  , stPostSleepingConstraints :: !Constraints
  , stPostDirty               :: !Bool -- local
    -- ^ Dirty when a constraint is added, used to prevent pointer update.
    -- Currently unused.
  , stPostOccursCheckDefs     :: !(Set QName) -- local
    -- ^ Definitions to be considered during occurs check.
    --   Initialized to the current mutual block before the check.
    --   During occurs check, we remove definitions from this set
    --   as soon we have checked them.
  , stPostSignature           :: !Signature
    -- ^ Declared identifiers of the current file.
    --   These will be serialized after successful type checking.
  , stPostModuleCheckpoints   :: !(Map ModuleName CheckpointId)
    -- ^ For each module remember the checkpoint corresponding to the orignal
    --   context of the module parameters.
  , stPostImportsDisplayForms :: !DisplayForms
    -- ^ Display forms we add for imported identifiers
  , stPostCurrentModule       :: !(Maybe ModuleName)
    -- ^ The current module is available after it has been type
    -- checked.
  , stPostInstanceDefs        :: !TempInstanceTable
  , stPostConcreteNames       :: !(Map Name [C.Name])
    -- ^ Map keeping track of concrete names assigned to each abstract name
    --   (can be more than one name in case the first one is shadowed)
  , stPostShadowingNames      :: !(Map Name [Name])
    -- ^ Map keeping track of which names could maybe be shadowed by
    -- another name
  , stPostStatistics          :: !Statistics
    -- ^ Counters to collect various statistics about meta variables etc.
    --   Only for current file.
  , stPostTCWarnings          :: ![TCWarning]
  , stPostMutualBlocks        :: !(Map MutualId MutualBlock)
  , stPostLocalBuiltins       :: !(BuiltinThings PrimFun)
  , stPostFreshMetaId         :: !MetaId
  , stPostFreshMutualId       :: !MutualId
  , stPostFreshProblemId      :: !ProblemId
  , stPostFreshCheckpointId   :: !CheckpointId
  , stPostFreshInt            :: !Int
  , stPostFreshNameId         :: !NameId
  , stPostAreWeCaching        :: !Bool
  , stPostConsideringInstance :: !Bool
  }

-- | A mutual block of names in the signature.
data MutualBlock = MutualBlock
  { mutualInfo  :: Info.MutualInfo
    -- ^ The original info of the mutual block.
  , mutualNames :: Set QName
  } deriving (Show, Eq)

instance Null MutualBlock where
  empty = MutualBlock empty empty

-- | A part of the state which is not reverted when an error is thrown
-- or the state is reset.
data PersistentTCState = PersistentTCSt
  { stDecodedModules    :: DecodedModules
  , stPersistentOptions :: CommandLineOptions
  , stInteractionOutputCallback  :: InteractionOutputCallback
    -- ^ Callback function to call when there is a response
    --   to give to the interactive frontend.
    --   See the documentation of 'InteractionOutputCallback'.
  , stBenchmark         :: !Benchmark
    -- ^ Structure to track how much CPU time was spent on which Agda phase.
    --   Needs to be a strict field to avoid space leaks!
  , stAccumStatistics   :: !Statistics
    -- ^ Should be strict field.
  , stLoadedFileCache   :: !(Maybe LoadedFileCache)
    -- ^ Cached typechecking state from the last loaded file.
    --   Should be Nothing when checking imports.
  , stPersistBackends   :: [Backend]
    -- ^ Current backends with their options
  }

data LoadedFileCache = LoadedFileCache
  { lfcCached  :: !CachedTypeCheckLog
  , lfcCurrent :: !CurrentTypeCheckLog
  }

-- | A log of what the type checker does and states after the action is
-- completed.  The cached version is stored first executed action first.
type CachedTypeCheckLog = [(TypeCheckAction, PostScopeState)]

-- | Like 'CachedTypeCheckLog', but storing the log for an ongoing type
-- checking of a module.  Stored in reverse order (last performed action
-- first).
type CurrentTypeCheckLog = [(TypeCheckAction, PostScopeState)]

-- | A complete log for a module will look like this:
--
--   * 'Pragmas'
--
--   * 'EnterSection', entering the main module.
--
--   * 'Decl'/'EnterSection'/'LeaveSection', for declarations and nested
--     modules
--
--   * 'LeaveSection', leaving the main module.
data TypeCheckAction
  = EnterSection !Info.ModuleInfo !ModuleName !A.Telescope
  | LeaveSection !ModuleName
  | Decl !A.Declaration
    -- ^ Never a Section or ScopeDecl
  | Pragmas !PragmaOptions

-- | Empty persistent state.

initPersistentState :: PersistentTCState
initPersistentState = PersistentTCSt
  { stPersistentOptions         = defaultOptions
  , stDecodedModules            = Map.empty
  , stInteractionOutputCallback = defaultInteractionOutputCallback
  , stBenchmark                 = empty
  , stAccumStatistics           = Map.empty
  , stLoadedFileCache           = Nothing
  , stPersistBackends           = []
  }

-- | Empty state of type checker.

initPreScopeState :: PreScopeState
initPreScopeState = PreScopeState
  { stPreTokens               = mempty
  , stPreImports              = emptySignature
  , stPreImportedModules      = Set.empty
  , stPreModuleToSource       = Map.empty
  , stPreVisitedModules       = Map.empty
  , stPreScope                = emptyScopeInfo
  , stPrePatternSyns          = Map.empty
  , stPrePatternSynImports    = Map.empty
  , stPreGeneralizedVars      = mempty
  , stPrePragmaOptions        = defaultInteractionOptions
  , stPreImportedBuiltins     = Map.empty
  , stPreImportedDisplayForms = HMap.empty
  , stPreImportedInstanceDefs = Map.empty
  , stPreForeignCode          = Map.empty
  , stPreFreshInteractionId   = 0
  , stPreImportedUserWarnings = Map.empty
  , stPreLocalUserWarnings    = Map.empty
  }

initPostScopeState :: PostScopeState
initPostScopeState = PostScopeState
  { stPostSyntaxInfo           = mempty
  , stPostDisambiguatedNames   = IntMap.empty
  , stPostMetaStore            = IntMap.empty
  , stPostInteractionPoints    = Map.empty
  , stPostAwakeConstraints     = []
  , stPostSleepingConstraints  = []
  , stPostDirty                = False
  , stPostOccursCheckDefs      = Set.empty
  , stPostSignature            = emptySignature
  , stPostModuleCheckpoints    = Map.empty
  , stPostImportsDisplayForms  = HMap.empty
  , stPostCurrentModule        = Nothing
  , stPostInstanceDefs         = (Map.empty , Set.empty)
  , stPostConcreteNames        = Map.empty
  , stPostShadowingNames       = Map.empty
  , stPostStatistics           = Map.empty
  , stPostTCWarnings           = []
  , stPostMutualBlocks         = Map.empty
  , stPostLocalBuiltins        = Map.empty
  , stPostFreshMetaId          = 0
  , stPostFreshMutualId        = 0
  , stPostFreshProblemId       = 1
  , stPostFreshCheckpointId    = 1
  , stPostFreshInt             = 0
  , stPostFreshNameId           = NameId 0 0
  , stPostAreWeCaching         = False
  , stPostConsideringInstance  = False
  }

initState :: TCState
initState = TCSt
  { stPreScopeState   = initPreScopeState
  , stPostScopeState  = initPostScopeState
  , stPersistentState = initPersistentState
  }

-- * st-prefixed lenses
------------------------------------------------------------------------

stTokens :: Lens' CompressedFile TCState
stTokens f s =
  f (stPreTokens (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreTokens = x}}

stImports :: Lens' Signature TCState
stImports f s =
  f (stPreImports (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreImports = x}}

stImportedModules :: Lens' (Set ModuleName) TCState
stImportedModules f s =
  f (stPreImportedModules (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreImportedModules = x}}

stModuleToSource :: Lens' ModuleToSource TCState
stModuleToSource f s =
  f (stPreModuleToSource (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreModuleToSource = x}}

stVisitedModules :: Lens' VisitedModules TCState
stVisitedModules f s =
  f (stPreVisitedModules (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreVisitedModules = x}}

stScope :: Lens' ScopeInfo TCState
stScope f s =
  f (stPreScope (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreScope = x}}

stPatternSyns :: Lens' A.PatternSynDefns TCState
stPatternSyns f s =
  f (stPrePatternSyns (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPrePatternSyns = x}}

stPatternSynImports :: Lens' A.PatternSynDefns TCState
stPatternSynImports f s =
  f (stPrePatternSynImports (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPrePatternSynImports = x}}

stGeneralizedVars :: Lens' (Maybe (Set QName)) TCState
stGeneralizedVars f s =
  f (stPreGeneralizedVars (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreGeneralizedVars = x}}

stPragmaOptions :: Lens' PragmaOptions TCState
stPragmaOptions f s =
  f (stPrePragmaOptions (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPrePragmaOptions = x}}

stImportedBuiltins :: Lens' (BuiltinThings PrimFun) TCState
stImportedBuiltins f s =
  f (stPreImportedBuiltins (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreImportedBuiltins = x}}

stForeignCode :: Lens' (Map BackendName [ForeignCode]) TCState
stForeignCode f s =
  f (stPreForeignCode (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreForeignCode = x}}

stFreshInteractionId :: Lens' InteractionId TCState
stFreshInteractionId f s =
  f (stPreFreshInteractionId (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreFreshInteractionId = x}}

stImportedUserWarnings :: Lens' (Map A.QName String) TCState
stImportedUserWarnings f s =
  f (stPreImportedUserWarnings (stPreScopeState s)) <&>
  \ x -> s {stPreScopeState = (stPreScopeState s) {stPreImportedUserWarnings = x}}

stLocalUserWarnings :: Lens' (Map A.QName String) TCState
stLocalUserWarnings f s =
  f (stPreLocalUserWarnings (stPreScopeState s)) <&>
  \ x -> s {stPreScopeState = (stPreScopeState s) {stPreLocalUserWarnings = x}}

getUserWarnings :: MonadTCState m => m (Map A.QName String)
getUserWarnings = do
  iuw <- useTC stImportedUserWarnings
  luw <- useTC stLocalUserWarnings
  return $ iuw `Map.union` luw

stBackends :: Lens' [Backend] TCState
stBackends f s =
  f (stPersistBackends (stPersistentState s)) <&>
  \x -> s {stPersistentState = (stPersistentState s) {stPersistBackends = x}}

stFreshNameId :: Lens' NameId TCState
stFreshNameId f s =
  f (stPostFreshNameId (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostFreshNameId = x}}

stSyntaxInfo :: Lens' CompressedFile TCState
stSyntaxInfo f s =
  f (stPostSyntaxInfo (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostSyntaxInfo = x}}

stDisambiguatedNames :: Lens' DisambiguatedNames TCState
stDisambiguatedNames f s =
  f (stPostDisambiguatedNames (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostDisambiguatedNames = x}}

stMetaStore :: Lens' MetaStore TCState
stMetaStore f s =
  f (stPostMetaStore (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostMetaStore = x}}

stInteractionPoints :: Lens' InteractionPoints TCState
stInteractionPoints f s =
  f (stPostInteractionPoints (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostInteractionPoints = x}}

stAwakeConstraints :: Lens' Constraints TCState
stAwakeConstraints f s =
  f (stPostAwakeConstraints (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostAwakeConstraints = x}}

stSleepingConstraints :: Lens' Constraints TCState
stSleepingConstraints f s =
  f (stPostSleepingConstraints (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostSleepingConstraints = x}}

stDirty :: Lens' Bool TCState
stDirty f s =
  f (stPostDirty (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostDirty = x}}

stOccursCheckDefs :: Lens' (Set QName) TCState
stOccursCheckDefs f s =
  f (stPostOccursCheckDefs (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostOccursCheckDefs = x}}

stSignature :: Lens' Signature TCState
stSignature f s =
  f (stPostSignature (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostSignature = x}}

stModuleCheckpoints :: Lens' (Map ModuleName CheckpointId) TCState
stModuleCheckpoints f s =
  f (stPostModuleCheckpoints (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostModuleCheckpoints = x}}

stImportsDisplayForms :: Lens' DisplayForms TCState
stImportsDisplayForms f s =
  f (stPostImportsDisplayForms (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostImportsDisplayForms = x}}

stImportedDisplayForms :: Lens' DisplayForms TCState
stImportedDisplayForms f s =
  f (stPreImportedDisplayForms (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreImportedDisplayForms = x}}

stCurrentModule :: Lens' (Maybe ModuleName) TCState
stCurrentModule f s =
  f (stPostCurrentModule (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostCurrentModule = x}}

stImportedInstanceDefs :: Lens' InstanceTable TCState
stImportedInstanceDefs f s =
  f (stPreImportedInstanceDefs (stPreScopeState s)) <&>
  \x -> s {stPreScopeState = (stPreScopeState s) {stPreImportedInstanceDefs = x}}

stInstanceDefs :: Lens' TempInstanceTable TCState
stInstanceDefs f s =
  f (stPostInstanceDefs (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostInstanceDefs = x}}

stConcreteNames :: Lens' (Map Name [C.Name]) TCState
stConcreteNames f s =
  f (stPostConcreteNames (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostConcreteNames = x}}

stShadowingNames :: Lens' (Map Name [Name]) TCState
stShadowingNames f s =
  f (stPostShadowingNames (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostShadowingNames = x}}

stStatistics :: Lens' Statistics TCState
stStatistics f s =
  f (stPostStatistics (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostStatistics = x}}

stTCWarnings :: Lens' [TCWarning] TCState
stTCWarnings f s =
  f (stPostTCWarnings (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostTCWarnings = x}}

stMutualBlocks :: Lens' (Map MutualId MutualBlock) TCState
stMutualBlocks f s =
  f (stPostMutualBlocks (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostMutualBlocks = x}}

stLocalBuiltins :: Lens' (BuiltinThings PrimFun) TCState
stLocalBuiltins f s =
  f (stPostLocalBuiltins (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostLocalBuiltins = x}}

stFreshMetaId :: Lens' MetaId TCState
stFreshMetaId f s =
  f (stPostFreshMetaId (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostFreshMetaId = x}}

stFreshMutualId :: Lens' MutualId TCState
stFreshMutualId f s =
  f (stPostFreshMutualId (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostFreshMutualId = x}}

stFreshProblemId :: Lens' ProblemId TCState
stFreshProblemId f s =
  f (stPostFreshProblemId (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostFreshProblemId = x}}

stFreshCheckpointId :: Lens' CheckpointId TCState
stFreshCheckpointId f s =
  f (stPostFreshCheckpointId (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostFreshCheckpointId = x}}

stFreshInt :: Lens' Int TCState
stFreshInt f s =
  f (stPostFreshInt (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostFreshInt = x}}

-- use @areWeCaching@ from the Caching module instead.
stAreWeCaching :: Lens' Bool TCState
stAreWeCaching f s =
  f (stPostAreWeCaching (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostAreWeCaching = x}}

stConsideringInstance :: Lens' Bool TCState
stConsideringInstance f s =
  f (stPostConsideringInstance (stPostScopeState s)) <&>
  \x -> s {stPostScopeState = (stPostScopeState s) {stPostConsideringInstance = x}}

stBuiltinThings :: TCState -> BuiltinThings PrimFun
stBuiltinThings s = (s^.stLocalBuiltins) `Map.union` (s^.stImportedBuiltins)


-- * Fresh things
------------------------------------------------------------------------

class Enum i => HasFresh i where
    freshLens :: Lens' i TCState
    nextFresh' :: i -> i
    nextFresh' = succ

nextFresh :: HasFresh i => TCState -> (i, TCState)
nextFresh s =
  let !c = s^.freshLens
  in (c, set freshLens (nextFresh' c) s)

fresh :: (HasFresh i, MonadTCState m) => m i
fresh =
    do  !s <- getTC
        let (!c , !s') = nextFresh s
        putTC s'
        return c

instance HasFresh MetaId where
  freshLens = stFreshMetaId

instance HasFresh MutualId where
  freshLens = stFreshMutualId

instance HasFresh InteractionId where
  freshLens = stFreshInteractionId

instance HasFresh NameId where
  freshLens = stFreshNameId
  -- nextFresh increments the current fresh name by 2 so @NameId@s used
  -- before caching starts do not overlap with the ones used after.
  nextFresh' = succ . succ

instance HasFresh Int where
  freshLens = stFreshInt

newtype ProblemId = ProblemId Nat
  deriving (Data, Eq, Ord, Enum, Real, Integral, Num)

-- TODO: 'Show' should output Haskell-parseable representations.
-- The following instance is deprecated, and Pretty[TCM] should be used
-- instead. Later, simply derive Show for this type.

-- ASR (28 December 2014). This instance is not used anymore (module
-- the test suite) when reporting errors. See Issue 1293.

-- This particular Show instance is ok because of the Num instance.
instance Show ProblemId where
  show (ProblemId n) = show n

instance Pretty ProblemId where
  pretty (ProblemId n) = pretty n

instance HasFresh ProblemId where
  freshLens = stFreshProblemId

newtype CheckpointId = CheckpointId Int
  deriving (Data, Eq, Ord, Enum, Real, Integral, Num)

instance Show CheckpointId where
  show (CheckpointId n) = show n

instance Pretty CheckpointId where
  pretty (CheckpointId n) = pretty n

instance HasFresh CheckpointId where
  freshLens = stFreshCheckpointId

freshName :: MonadTCState m => Range -> String -> m Name
freshName r s = do
  i <- fresh
  return $ mkName r i s

freshNoName :: MonadTCState m => Range -> m Name
freshNoName r =
    do  i <- fresh
        return $ Name i (C.NoName noRange i) r noFixity' False

freshNoName_ :: MonadTCState m => m Name
freshNoName_ = freshNoName noRange

freshRecordName :: MonadTCState m => m Name
freshRecordName = do
  i <- fresh
  return $ Name i (C.Name noRange C.NotInScope [C.Id "r"]) noRange noFixity' True

-- | Create a fresh name from @a@.
class FreshName a where
  freshName_ :: MonadTCState m => a -> m Name

instance FreshName (Range, String) where
  freshName_ = uncurry freshName

instance FreshName String where
  freshName_ = freshName noRange

instance FreshName Range where
  freshName_ = freshNoName

instance FreshName () where
  freshName_ () = freshNoName_

---------------------------------------------------------------------------
-- ** Managing file names
---------------------------------------------------------------------------

-- | Maps top-level module names to the corresponding source file
-- names.

type ModuleToSource = Map TopLevelModuleName AbsolutePath

-- | Maps source file names to the corresponding top-level module
-- names.

type SourceToModule = Map AbsolutePath TopLevelModuleName

-- | Creates a 'SourceToModule' map based on 'stModuleToSource'.
--
--   O(n log n).
--
--   For a single reverse lookup in 'stModuleToSource',
--   rather use 'lookupModuleFromSourse'.

sourceToModule :: TCM SourceToModule
sourceToModule =
  Map.fromList
     .  List.map (\(m, f) -> (f, m))
     .  Map.toList
    <$> useTC stModuleToSource

-- | Lookup an 'AbsolutePath' in 'sourceToModule'.
--
--   O(n).

lookupModuleFromSource :: AbsolutePath -> TCM (Maybe TopLevelModuleName)
lookupModuleFromSource f =
  fmap fst . List.find ((f ==) . snd) . Map.toList <$> useTC stModuleToSource

---------------------------------------------------------------------------
-- ** Interface
---------------------------------------------------------------------------

data ModuleInfo = ModuleInfo
  { miInterface  :: Interface
  , miWarnings   :: Bool
    -- ^ 'True' if warnings were encountered when the module was type
    -- checked.
  , miPrimitive  :: Bool
    -- ^ 'True' if the module is a primitive module, which should always
    -- be importable.
  }

-- Note that the use of 'C.TopLevelModuleName' here is a potential
-- performance problem, because these names do not contain unique
-- identifiers.

type VisitedModules = Map C.TopLevelModuleName ModuleInfo
type DecodedModules = Map C.TopLevelModuleName Interface

data ForeignCode = ForeignCode Range String
  deriving Show

data Interface = Interface
  { iSourceHash      :: Hash
    -- ^ Hash of the source code.
  , iSource          :: Text
    -- ^ The source code. The source code is stored so that the HTML
    -- and LaTeX backends can generate their output without having to
    -- re-read the (possibly out of date) source code.
  , iFileType        :: FileType
    -- ^ Source file type, determined from the file extension
  , iImportedModules :: [(ModuleName, Hash)]
    -- ^ Imported modules and their hashes.
  , iModuleName      :: ModuleName
    -- ^ Module name of this interface.
  , iScope           :: Map ModuleName Scope
    -- ^ Scope defined by this module.
    --
    --   Andreas, AIM XX: Too avoid duplicate serialization, this field is
    --   not serialized, so if you deserialize an interface, @iScope@
    --   will be empty.
    --   But 'constructIScope' constructs 'iScope' from 'iInsideScope'.
  , iInsideScope     :: ScopeInfo
    -- ^ Scope after we loaded this interface.
    --   Used in 'Agda.Interaction.BasicOps.AtTopLevel'
    --   and     'Agda.Interaction.CommandLine.interactionLoop'.
  , iSignature       :: Signature
  , iDisplayForms    :: DisplayForms
    -- ^ Display forms added for imported identifiers.
  , iUserWarnings    :: Map A.QName String
    -- ^ User warnings for imported identifiers
  , iBuiltin         :: BuiltinThings (String, QName)
  , iForeignCode     :: Map BackendName [ForeignCode]
  , iHighlighting    :: HighlightingInfo
  , iPragmaOptions   :: [OptionsPragma]
    -- ^ Pragma options set in the file.
  , iOptionsUsed     :: PragmaOptions
    -- ^ Options/features used when checking the file (can be different
    --   from options set directly in the file).
  , iPatternSyns     :: A.PatternSynDefns
  , iWarnings        :: [TCWarning]
  }
  deriving Show

instance Pretty Interface where
  pretty (Interface
            sourceH source fileT importedM moduleN scope insideS signature
            display userwarn builtin foreignCode highlighting pragmaO
            oUsed patternS warnings) =
    hang "Interface" 2 $ vcat
      [ "source hash:"         <+> (pretty . show) sourceH
      , "source:"              $$  nest 2 (text $ T.unpack source)
      , "file type:"           <+> (pretty . show) fileT
      , "imported modules:"    <+> (pretty . show) importedM
      , "module name:"         <+> pretty moduleN
      , "scope:"               <+> (pretty . show) scope
      , "inside scope:"        <+> (pretty . show) insideS
      , "signature:"           <+> (pretty . show) signature
      , "display:"             <+> (pretty . show) display
      , "user warnings:"       <+> (pretty . show) userwarn
      , "builtin:"             <+> (pretty . show) builtin
      , "Foreign code:"        <+> (pretty . show) foreignCode
      , "highlighting:"        <+> (pretty . show) highlighting
      , "pragma options:"      <+> (pretty . show) pragmaO
      , "options used:"        <+> (pretty . show) oUsed
      , "pattern syns:"        <+> (pretty . show) patternS
      , "warnings:"            <+> (pretty . show) warnings
      ]

-- | Combines the source hash and the (full) hashes of the imported modules.
iFullHash :: Interface -> Hash
iFullHash i = combineHashes $ iSourceHash i : List.map snd (iImportedModules i)

---------------------------------------------------------------------------
-- ** Closure
---------------------------------------------------------------------------

data Closure a = Closure
  { clSignature        :: Signature
  , clEnv              :: TCEnv
  , clScope            :: ScopeInfo
  , clModuleCheckpoints :: Map ModuleName CheckpointId
  , clValue            :: a
  }
    deriving (Data, Functor, Foldable)

instance Show a => Show (Closure a) where
  show cl = "Closure { clValue = " ++ show (clValue cl) ++ " }"

instance HasRange a => HasRange (Closure a) where
    getRange = getRange . clValue

buildClosure :: a -> TCM (Closure a)
buildClosure x = do
    env   <- askTC
    sig   <- useTC stSignature
    scope <- useTC stScope
    cps   <- useTC stModuleCheckpoints
    return $ Closure sig env scope cps x

---------------------------------------------------------------------------
-- ** Constraints
---------------------------------------------------------------------------

type Constraints = [ProblemConstraint]

data ProblemConstraint = PConstr
  { constraintProblems :: Set ProblemId
  , theConstraint      :: Closure Constraint
  }
  deriving (Data, Show)

instance HasRange ProblemConstraint where
  getRange = getRange . theConstraint

data Constraint
  = ValueCmp Comparison Type Term Term
  | ValueCmpOnFace Comparison Term Type Term Term
  | ElimCmp [Polarity] [IsForced] Type Term [Elim] [Elim]
  | TypeCmp Comparison Type Type
  | TelCmp Type Type Comparison Telescope Telescope -- ^ the two types are for the error message only
  | SortCmp Comparison Sort Sort
  | LevelCmp Comparison Level Level
--  | ShortCut MetaId Term Type
--    -- ^ A delayed instantiation.  Replaces @ValueCmp@ in 'postponeTypeCheckingProblem'.
  | HasBiggerSort Sort
  | HasPTSRule Sort (Abs Sort)
  | UnBlock MetaId
  | Guarded Constraint ProblemId
  | IsEmpty Range Type
    -- ^ The range is the one of the absurd pattern.
  | CheckSizeLtSat Term
    -- ^ Check that the 'Term' is either not a SIZELT or a non-empty SIZELT.
  | FindInstance MetaId (Maybe MetaId) (Maybe [Candidate])
    -- ^ the first argument is the instance argument, the second one is the meta
    --   on which the constraint may be blocked on and the third one is the list
    --   of candidates (or Nothing if we haven’t determined the list of
    --   candidates yet)
  | CheckFunDef Delayed Info.DefInfo QName [A.Clause]
  | UnquoteTactic (Maybe MetaId) Term Term Type   -- ^ First argument is computation and the others are hole and goal type
  deriving (Data, Show)

instance HasRange Constraint where
  getRange (IsEmpty r t) = r
  getRange _ = noRange
{- no Range instances for Term, Type, Elm, Tele, Sort, Level, MetaId
  getRange (ValueCmp cmp a u v) = getRange (a,u,v)
  getRange (ElimCmp pol a v es es') = getRange (a,v,es,es')
  getRange (TypeCmp cmp a b) = getRange (a,b)
  getRange (TelCmp a b cmp tel tel') = getRange (a,b,tel,tel')
  getRange (SortCmp cmp s s') = getRange (s,s')
  getRange (LevelCmp cmp l l') = getRange (l,l')
  getRange (UnBlock x) = getRange x
  getRange (Guarded c pid) = getRange c
  getRange (FindInstance x cands) = getRange x
-}

instance Free Constraint where
  freeVars' c =
    case c of
      ValueCmp _ t u v      -> freeVars' (t, (u, v))
      ValueCmpOnFace _ p t u v -> freeVars' (p, (t, (u, v)))
      ElimCmp _ _ t u es es'  -> freeVars' ((t, u), (es, es'))
      TypeCmp _ t t'        -> freeVars' (t, t')
      TelCmp _ _ _ tel tel' -> freeVars' (tel, tel')
      SortCmp _ s s'        -> freeVars' (s, s')
      LevelCmp _ l l'       -> freeVars' (l, l')
      UnBlock _             -> mempty
      Guarded c _           -> freeVars' c
      IsEmpty _ t           -> freeVars' t
      CheckSizeLtSat u      -> freeVars' u
      FindInstance _ _ cs   -> freeVars' cs
      CheckFunDef _ _ _ _   -> mempty
      HasBiggerSort s       -> freeVars' s
      HasPTSRule s1 s2      -> freeVars' (s1 , s2)
      UnquoteTactic _ t h g -> freeVars' (t, (h, g))

instance TermLike Constraint where
  foldTerm f = \case
      ValueCmp _ t u v       -> foldTerm f (t, u, v)
      ValueCmpOnFace _ p t u v -> foldTerm f (p, t, u, v)
      ElimCmp _ _ t u es es' -> foldTerm f (t, u, es, es')
      TypeCmp _ t t'         -> foldTerm f (t, t')
      LevelCmp _ l l'        -> foldTerm f (l, l')
      IsEmpty _ t            -> foldTerm f t
      CheckSizeLtSat u       -> foldTerm f u
      UnquoteTactic _ t h g  -> foldTerm f (t, h, g)
      Guarded c _            -> foldTerm f c
      TelCmp _ _ _ tel1 tel2 -> foldTerm f (tel1, tel2)
      SortCmp _ s1 s2        -> foldTerm f (s1, s2)
      UnBlock _              -> mempty
      FindInstance _ _ _     -> mempty
      CheckFunDef _ _ _ _    -> mempty
      HasBiggerSort s        -> foldTerm f s
      HasPTSRule s1 s2       -> foldTerm f (s1, s2)
  traverseTermM f c = __IMPOSSIBLE__ -- Not yet implemented


data Comparison = CmpEq | CmpLeq
  deriving (Eq, Data, Show)

instance Pretty Comparison where
  pretty CmpEq  = "="
  pretty CmpLeq = "=<"

-- | An extension of 'Comparison' to @>=@.
data CompareDirection = DirEq | DirLeq | DirGeq
  deriving (Eq, Show)

instance Pretty CompareDirection where
  pretty = text . \case
    DirEq  -> "="
    DirLeq -> "=<"
    DirGeq -> ">="

-- | Embed 'Comparison' into 'CompareDirection'.
fromCmp :: Comparison -> CompareDirection
fromCmp CmpEq  = DirEq
fromCmp CmpLeq = DirLeq

-- | Flip the direction of comparison.
flipCmp :: CompareDirection -> CompareDirection
flipCmp DirEq  = DirEq
flipCmp DirLeq = DirGeq
flipCmp DirGeq = DirLeq

-- | Turn a 'Comparison' function into a 'CompareDirection' function.
--
--   Property: @dirToCmp f (fromCmp cmp) = f cmp@
dirToCmp :: (Comparison -> a -> a -> c) -> CompareDirection -> a -> a -> c
dirToCmp cont DirEq  = cont CmpEq
dirToCmp cont DirLeq = cont CmpLeq
dirToCmp cont DirGeq = flip $ cont CmpLeq

---------------------------------------------------------------------------
-- * Open things
---------------------------------------------------------------------------

-- | A thing tagged with the context it came from.
data Open a = OpenThing { openThingCheckpoint :: CheckpointId, openThing :: a }
    deriving (Data, Show, Functor, Foldable, Traversable)

instance Decoration Open where
  traverseF f (OpenThing cp x) = OpenThing cp <$> f x

---------------------------------------------------------------------------
-- * Judgements
--
-- Used exclusively for typing of meta variables.
---------------------------------------------------------------------------

-- | Parametrized since it is used without MetaId when creating a new meta.
data Judgement a
  = HasType { jMetaId :: a, jMetaType :: Type }
  | IsSort  { jMetaId :: a, jMetaType :: Type } -- Andreas, 2011-04-26: type needed for higher-order sort metas

instance Show a => Show (Judgement a) where
    show (HasType a t) = show a ++ " : " ++ show t
    show (IsSort  a t) = show a ++ " :sort " ++ show t

-----------------------------------------------------------------------------
-- ** Generalizable variables
-----------------------------------------------------------------------------

data DoGeneralize = YesGeneralize | NoGeneralize
  deriving (Eq, Ord, Show, Data)

-- | The value of a generalizable variable. This is created to be a
--   generalizable meta before checking the type to be generalized.
data GeneralizedValue = GeneralizedValue
  { genvalCheckpoint :: CheckpointId
  , genvalTerm       :: Term
  , genvalType       :: Type
  } deriving (Show, Data)

---------------------------------------------------------------------------
-- ** Meta variables
---------------------------------------------------------------------------

data MetaVariable =
        MetaVar { mvInfo          :: MetaInfo
                , mvPriority      :: MetaPriority -- ^ some metavariables are more eager to be instantiated
                , mvPermutation   :: Permutation
                  -- ^ a metavariable doesn't have to depend on all variables
                  --   in the context, this "permutation" will throw away the
                  --   ones it does not depend on
                , mvJudgement     :: Judgement MetaId
                , mvInstantiation :: MetaInstantiation
                , mvListeners     :: Set Listener -- ^ meta variables scheduled for eta-expansion but blocked by this one
                , mvFrozen        :: Frozen -- ^ are we past the point where we can instantiate this meta variable?
                }

data Listener = EtaExpand MetaId
              | CheckConstraint Nat ProblemConstraint

instance Eq Listener where
  EtaExpand       x   == EtaExpand       y   = x == y
  CheckConstraint x _ == CheckConstraint y _ = x == y
  _ == _ = False

instance Ord Listener where
  EtaExpand       x   `compare` EtaExpand       y   = x `compare` y
  CheckConstraint x _ `compare` CheckConstraint y _ = x `compare` y
  EtaExpand{} `compare` CheckConstraint{} = LT
  CheckConstraint{} `compare` EtaExpand{} = GT

-- | Frozen meta variable cannot be instantiated by unification.
--   This serves to prevent the completion of a definition by its use
--   outside of the current block.
--   (See issues 118, 288, 399).
data Frozen
  = Frozen        -- ^ Do not instantiate.
  | Instantiable
    deriving (Eq, Show)

data MetaInstantiation
        = InstV [Arg String] Term -- ^ solved by term (abstracted over some free variables)
        | Open               -- ^ unsolved
        | OpenInstance       -- ^ open, to be instantiated by instance search
        | BlockedConst Term  -- ^ solution blocked by unsolved constraints
        | PostponedTypeCheckingProblem (Closure TypeCheckingProblem) (TCM Bool)

-- | Solving a 'CheckArgs' constraint may or may not check the target type. If
--   it did, it returns a handle to any unsolved constraints.
data CheckedTarget = CheckedTarget (Maybe ProblemId)
                   | NotCheckedTarget

data TypeCheckingProblem
  = CheckExpr Comparison A.Expr Type
  | CheckArgs ExpandHidden Range [NamedArg A.Expr] Type Type ([Maybe Range] -> Elims -> Type -> CheckedTarget -> TCM Term)
  | CheckProjAppToKnownPrincipalArg Comparison A.Expr ProjOrigin (NonemptyList QName) A.Args Type Int Term Type
  | CheckLambda Comparison (Arg ([WithHiding Name], Maybe Type)) A.Expr Type
    -- ^ @(λ (xs : t₀) → e) : t@
    --   This is not an instance of 'CheckExpr' as the domain type
    --   has already been checked.
    --   For example, when checking
    --     @(λ (x y : Fin _) → e) : (x : Fin n) → ?@
    --   we want to postpone @(λ (y : Fin n) → e) : ?@ where @Fin n@
    --   is a 'Type' rather than an 'A.Expr'.
  | DoQuoteTerm Comparison Term Type -- ^ Quote the given term and check type against `Term`

instance Show MetaInstantiation where
  show (InstV tel t) = "InstV " ++ show tel ++ " (" ++ show t ++ ")"
  show Open      = "Open"
  show OpenInstance = "OpenInstance"
  show (BlockedConst t) = "BlockedConst (" ++ show t ++ ")"
  show (PostponedTypeCheckingProblem{}) = "PostponedTypeCheckingProblem (...)"

-- | Meta variable priority:
--   When we have an equation between meta-variables, which one
--   should be instantiated?
--
--   Higher value means higher priority to be instantiated.
newtype MetaPriority = MetaPriority Int
    deriving (Eq , Ord , Show)

data RunMetaOccursCheck
  = RunMetaOccursCheck
  | DontRunMetaOccursCheck
  deriving (Eq , Ord , Show)

-- | @MetaInfo@ is cloned from one meta to the next during pruning.
data MetaInfo = MetaInfo
  { miClosRange       :: Closure Range -- TODO: Not so nice. But we want both to have the environment of the meta (Closure) and its range.
--  , miRelevance       :: Relevance          -- ^ Created in irrelevant position?
  , miMetaOccursCheck :: RunMetaOccursCheck -- ^ Run the extended occurs check that goes in definitions?
  , miNameSuggestion  :: MetaNameSuggestion
    -- ^ Used for printing.
    --   @Just x@ if meta-variable comes from omitted argument with name @x@.
  , miGeneralizable   :: Arg DoGeneralize
    -- ^ Should this meta be generalized if unsolved? If so, at what ArgInfo?
  }

-- | Name suggestion for meta variable.  Empty string means no suggestion.
type MetaNameSuggestion = String

-- | For printing, we couple a meta with its name suggestion.
data NamedMeta = NamedMeta
  { nmSuggestion :: MetaNameSuggestion
  , nmid         :: MetaId
  }

instance Pretty NamedMeta where
  pretty (NamedMeta "" x) = pretty x
  pretty (NamedMeta "_" x) = pretty x
  pretty (NamedMeta s  x) = text $ "_" ++ s ++ prettyShow x

type MetaStore = IntMap MetaVariable

instance HasRange MetaInfo where
  getRange = clValue . miClosRange

instance HasRange MetaVariable where
    getRange m = getRange $ getMetaInfo m

instance SetRange MetaInfo where
  setRange r m = m { miClosRange = (miClosRange m) { clValue = r }}

instance SetRange MetaVariable where
  setRange r m = m { mvInfo = setRange r (mvInfo m) }

normalMetaPriority :: MetaPriority
normalMetaPriority = MetaPriority 0

lowMetaPriority :: MetaPriority
lowMetaPriority = MetaPriority (-10)

highMetaPriority :: MetaPriority
highMetaPriority = MetaPriority 10

getMetaInfo :: MetaVariable -> Closure Range
getMetaInfo = miClosRange . mvInfo

getMetaScope :: MetaVariable -> ScopeInfo
getMetaScope m = clScope $ getMetaInfo m

getMetaEnv :: MetaVariable -> TCEnv
getMetaEnv m = clEnv $ getMetaInfo m

getMetaSig :: MetaVariable -> Signature
getMetaSig m = clSignature $ getMetaInfo m

getMetaRelevance :: MetaVariable -> Relevance
getMetaRelevance = envRelevance . getMetaEnv

getMetaModality :: MetaVariable -> Modality
getMetaModality = envModality . getMetaEnv

-- Lenses

metaFrozen :: Lens' Frozen MetaVariable
metaFrozen f mv = f (mvFrozen mv) <&> \ x -> mv { mvFrozen = x }

---------------------------------------------------------------------------
-- ** Interaction meta variables
---------------------------------------------------------------------------

-- | Interaction points are created by the scope checker who sets the range.
--   The meta variable is created by the type checker and then hooked up to the
--   interaction point.
data InteractionPoint = InteractionPoint
  { ipRange :: Range        -- ^ The position of the interaction point.
  , ipMeta  :: Maybe MetaId -- ^ The meta variable, if any, holding the type etc.
  , ipSolved:: Bool         -- ^ Has this interaction point already been solved?
  , ipClause:: IPClause
      -- ^ The clause of the interaction point (if any).
      --   Used for case splitting.
  }

instance Eq InteractionPoint where (==) = (==) `on` ipMeta

-- | Data structure managing the interaction points.
--
--   We never remove interaction points from this map, only set their
--   'ipSolved' to @True@.  (Issue #2368)
type InteractionPoints = Map InteractionId InteractionPoint

-- | Which clause is an interaction point located in?
data IPClause = IPClause
  { ipcQName    :: QName  -- ^ The name of the function.
  , ipcClauseNo :: Int    -- ^ The number of the clause of this function.
  , ipcClause   :: A.RHS  -- ^ The original AST clause rhs.
  }
  | IPNoClause -- ^ The interaction point is not in the rhs of a clause.
  deriving Data

instance Eq IPClause where
  IPNoClause     == IPNoClause       = True
  IPClause x i _ == IPClause x' i' _ = x == x' && i == i'
  _              == _                = False

---------------------------------------------------------------------------
-- ** Signature
---------------------------------------------------------------------------

data Signature = Sig
      { _sigSections    :: Sections
      , _sigDefinitions :: Definitions
      , _sigRewriteRules:: RewriteRuleMap  -- ^ The rewrite rules defined in this file.
      }
  deriving (Data, Show)

sigSections :: Lens' Sections Signature
sigSections f s =
  f (_sigSections s) <&>
  \x -> s {_sigSections = x}

sigDefinitions :: Lens' Definitions Signature
sigDefinitions f s =
  f (_sigDefinitions s) <&>
  \x -> s {_sigDefinitions = x}

sigRewriteRules :: Lens' RewriteRuleMap Signature
sigRewriteRules f s =
  f (_sigRewriteRules s) <&>
  \x -> s {_sigRewriteRules = x}

type Sections    = Map ModuleName Section
type Definitions = HashMap QName Definition
type RewriteRuleMap = HashMap QName RewriteRules
type DisplayForms = HashMap QName [LocalDisplayForm]

newtype Section = Section { _secTelescope :: Telescope }
  deriving (Data, Show)

instance Pretty Section where
  pretty = pretty . _secTelescope

secTelescope :: Lens' Telescope Section
secTelescope f s =
  f (_secTelescope s) <&>
  \x -> s {_secTelescope = x}

emptySignature :: Signature
emptySignature = Sig Map.empty HMap.empty HMap.empty

-- | A @DisplayForm@ is in essence a rewrite rule
--   @
--      q ts --> dt
--   @
--   for a defined symbol (could be a constructor as well) @q@.
--   The right hand side is a 'DisplayTerm' which is used to
--   'reify' to a more readable 'Abstract.Syntax'.
--
--   The patterns @ts@ are just terms, but @var 0@ is interpreted
--   as a hole.  Each occurrence of @var 0@ is a new hole (pattern var).
--   For each *occurrence* of @var0@ the rhs @dt@ has a free variable.
--   These are instantiated when matching a display form against a
--   term @q vs@ succeeds.
data DisplayForm = Display
  { dfFreeVars :: Nat
    -- ^ Number @n@ of free variables in 'dfRHS'.
  , dfPats     :: Elims
    -- ^ Left hand side patterns, where @var 0@ stands for a pattern
    --   variable.  There should be @n@ occurrences of @var0@ in
    --   'dfPats'.
    --   The 'ArgInfo' is ignored in these patterns.
  , dfRHS      :: DisplayTerm
    -- ^ Right hand side, with @n@ free variables.
  }
  deriving (Data, Show)

type LocalDisplayForm = Open DisplayForm

-- | A structured presentation of a 'Term' for reification into
--   'Abstract.Syntax'.
data DisplayTerm
  = DWithApp DisplayTerm [DisplayTerm] Elims
    -- ^ @(f vs | ws) es@.
    --   The first 'DisplayTerm' is the parent function @f@ with its args @vs@.
    --   The list of 'DisplayTerm's are the with expressions @ws@.
    --   The 'Elims' are additional arguments @es@
    --   (possible in case the with-application is of function type)
    --   or projections (if it is of record type).
  | DCon ConHead ConInfo [Arg DisplayTerm]
    -- ^ @c vs@.
  | DDef QName [Elim' DisplayTerm]
    -- ^ @d vs@.
  | DDot Term
    -- ^ @.v@.
  | DTerm Term
    -- ^ @v@.
  deriving (Data, Show)

instance Free DisplayForm where
  freeVars' (Display n ps t) = bind (freeVars' ps) `mappend` bind' n (freeVars' t)

instance Free DisplayTerm where
  freeVars' (DWithApp t ws es) = freeVars' (t, (ws, es))
  freeVars' (DCon _ _ vs)      = freeVars' vs
  freeVars' (DDef _ es)        = freeVars' es
  freeVars' (DDot v)           = freeVars' v
  freeVars' (DTerm v)          = freeVars' v

instance Pretty DisplayTerm where
  prettyPrec p v =
    case v of
      DTerm v          -> prettyPrec p v
      DDot v           -> "." P.<> prettyPrec 10 v
      DDef f es        -> pretty f `pApp` es
      DCon c _ vs      -> pretty (conName c) `pApp` map Apply vs
      DWithApp h ws es ->
        mparens (p > 0)
          (sep [ pretty h
              , nest 2 $ fsep [ "|" <+> pretty w | w <- ws ] ])
        `pApp` es
    where
      pApp d els = mparens (not (null els) && p > 9) $
                   sep [d, nest 2 $ fsep (map (prettyPrec 10) els)]

-- | By default, we have no display form.
defaultDisplayForm :: QName -> [LocalDisplayForm]
defaultDisplayForm c = []

defRelevance :: Definition -> Relevance
defRelevance = getRelevance . defArgInfo

-- | Non-linear (non-constructor) first-order pattern.
data NLPat
  = PVar !Int [Arg Int]
    -- ^ Matches anything (modulo non-linearity) that only contains bound
    --   variables that occur in the given arguments.
  | PWild
    -- ^ Matches anything (e.g. irrelevant terms).
  | PDef QName PElims
    -- ^ Matches @f es@
  | PLam ArgInfo (Abs NLPat)
    -- ^ Matches @λ x → t@
  | PPi (Dom NLPType) (Abs NLPType)
    -- ^ Matches @(x : A) → B@
  | PBoundVar {-# UNPACK #-} !Int PElims
    -- ^ Matches @x es@ where x is a lambda-bound variable
  | PTerm Term
    -- ^ Matches the term modulo β (ideally βη).
  deriving (Data, Show)
type PElims = [Elim' NLPat]

data NLPType = NLPType
  { nlpTypeLevel :: NLPat  -- always PWild or PVar (with all bound variables in scope)
  , nlpTypeUnEl  :: NLPat
  } deriving (Data, Show)

type RewriteRules = [RewriteRule]

-- | Rewrite rules can be added independently from function clauses.
data RewriteRule = RewriteRule
  { rewName    :: QName      -- ^ Name of rewrite rule @q : Γ → f ps ≡ rhs@
                             --   where @≡@ is the rewrite relation.
  , rewContext :: Telescope  -- ^ @Γ@.
  , rewHead    :: QName      -- ^ @f@.
  , rewPats    :: PElims     -- ^ @Γ ⊢ f ps : t@.
  , rewRHS     :: Term       -- ^ @Γ ⊢ rhs : t@.
  , rewType    :: Type       -- ^ @Γ ⊢ t@.
  }
    deriving (Data, Show)

data Definition = Defn
  { defArgInfo        :: ArgInfo -- ^ Hiding should not be used.
  , defName           :: QName
  , defType           :: Type    -- ^ Type of the lifted definition.
  , defPolarity       :: [Polarity]
    -- ^ Variance information on arguments of the definition.
    --   Does not include info for dropped parameters to
    --   projection(-like) functions and constructors.
  , defArgOccurrences :: [Occurrence]
    -- ^ Positivity information on arguments of the definition.
    --   Does not include info for dropped parameters to
    --   projection(-like) functions and constructors.

    --   Sometimes Agda looks up 'Occurrence's in these lists based on
    --   their position, so one might consider replacing the list
    --   with, say, an 'IntMap'. However, presumably these lists tend
    --   to be short, in which case 'IntMap's could be slower than
    --   lists. For instance, at one point the longest list
    --   encountered for the standard library (in serialised
    --   interfaces) had length 27. Distribution:
    --
    --   Length, number of lists
    --   -----------------------
    --
    --    0, 2444
    --    1,  721
    --    2,  433
    --    3,  668
    --    4,  602
    --    5,  624
    --    6,  626
    --    7,  484
    --    8,  375
    --    9,  264
    --   10,  305
    --   11,  188
    --   12,  171
    --   13,  108
    --   14,   84
    --   15,   80
    --   16,   38
    --   17,   23
    --   18,   16
    --   19,    8
    --   20,    7
    --   21,    5
    --   22,    2
    --   23,    3
    --   27,    1

  , defArgGeneralizable :: NumGeneralizableArgs
    -- ^ How many arguments should be generalised.
  , defGeneralizedParams :: [Maybe Name]
    -- ^ Gives the name of the (bound variable) parameter for named generalized
    --   parameters. This is needed to bring it into scope when type checking
    --   the data/record definition corresponding to a type with generalized
    --   parameters.
  , defDisplay        :: [LocalDisplayForm]
  , defMutual         :: MutualId
  , defCompiledRep    :: CompiledRepresentation
  , defInstance       :: Maybe QName
    -- ^ @Just q@ when this definition is an instance of class q
  , defCopy           :: Bool
    -- ^ Has this function been created by a module
                         -- instantiation?
  , defMatchable      :: Bool
    -- ^ Is the def matched against in a rewrite rule?
  , defNoCompilation  :: Bool
    -- ^ should compilers skip this? Used for e.g. cubical's comp
  , defInjective      :: Bool
    -- ^ Should the def be treated as injective by the pattern matching unifier?
  , theDef            :: Defn
  }
    deriving (Data, Show)

data NumGeneralizableArgs
  = NoGeneralizableArgs
  | SomeGeneralizableArgs Int
    -- ^ When lambda-lifting new args are generalizable if
    --   'SomeGeneralizableArgs', also when the number is zero.
  deriving (Data, Show)

theDefLens :: Lens' Defn Definition
theDefLens f d = f (theDef d) <&> \ df -> d { theDef = df }

-- | Create a definition with sensible defaults.
defaultDefn :: ArgInfo -> QName -> Type -> Defn -> Definition
defaultDefn info x t def = Defn
  { defArgInfo        = info
  , defName           = x
  , defType           = t
  , defPolarity       = []
  , defArgOccurrences = []
  , defArgGeneralizable = NoGeneralizableArgs
  , defGeneralizedParams = []
  , defDisplay        = defaultDisplayForm x
  , defMutual         = 0
  , defCompiledRep    = noCompiledRep
  , defInstance       = Nothing
  , defCopy           = False
  , defMatchable      = False
  , defNoCompilation  = False
  , defInjective      = False
  , theDef            = def
  }

-- | Polarity for equality and subtype checking.
data Polarity
  = Covariant      -- ^ monotone
  | Contravariant  -- ^ antitone
  | Invariant      -- ^ no information (mixed variance)
  | Nonvariant     -- ^ constant
  deriving (Data, Show, Eq)

instance Pretty Polarity where
  pretty = text . \case
    Covariant     -> "+"
    Contravariant -> "-"
    Invariant     -> "*"
    Nonvariant    -> "_"

-- | Information about whether an argument is forced by the type of a function.
data IsForced
  = Forced
  | NotForced
  deriving (Data, Show, Eq)

-- | The backends are responsible for parsing their own pragmas.
data CompilerPragma = CompilerPragma Range String
  deriving (Data, Show, Eq)

instance HasRange CompilerPragma where
  getRange (CompilerPragma r _) = r

type BackendName    = String

jsBackendName, ghcBackendName :: BackendName
jsBackendName  = "JS"
ghcBackendName = "GHC"

type CompiledRepresentation = Map BackendName [CompilerPragma]

noCompiledRep :: CompiledRepresentation
noCompiledRep = Map.empty

-- A face represented as a list of equality constraints.
-- (r,False) ↦ (r = i0)
-- (r,True ) ↦ (r = i1)
type Face = [(Term,Bool)]

-- | An alternative representation of partial elements in a telescope:
--   Γ ⊢ λ Δ. [φ₁ u₁, ... , φₙ uₙ] : Δ → PartialP (∨_ᵢ φᵢ) T
--   see cubicaltt paper (however we do not store the type T).
data System = System
  { systemTel :: Telescope
    -- ^ the telescope Δ, binding vars for the clauses, Γ ⊢ Δ
  , systemClauses :: [(Face,Term)]
    -- ^ a system [φ₁ u₁, ... , φₙ uₙ] where Γ, Δ ⊢ φᵢ and Γ, Δ, φᵢ ⊢ uᵢ
  } deriving (Data, Show)

-- | Additional information for extended lambdas.
data ExtLamInfo = ExtLamInfo
  { extLamModule    :: ModuleName
    -- ^ For complicated reasons the scope checker decides the QName of a
    --   pattern lambda, and thus its module. We really need to decide the
    --   module during type checking though, since if the lambda appears in a
    --   refined context the module picked by the scope checker has very much
    --   the wrong parameters.
  , extLamSys :: !(Maybe System)
  } deriving (Data, Show)

modifySystem :: (System -> System) -> ExtLamInfo -> ExtLamInfo
modifySystem f e = let !e' = e { extLamSys = f <$> extLamSys e } in e'

-- | Additional information for projection 'Function's.
data Projection = Projection
  { projProper    :: Maybe QName
    -- ^ @Nothing@ if only projection-like, @Just r@ if record projection.
    --   The @r@ is the name of the record type projected from.
    --   This field is updated by module application.
  , projOrig      :: QName
    -- ^ The original projection name
    --   (current name could be from module application).
  , projFromType  :: Arg QName
    -- ^ Type projected from. Original record type if @projProper = Just{}@.
    --   Also stores @ArgInfo@ of the principal argument.
    --   This field is unchanged by module application.
  , projIndex     :: Int
    -- ^ Index of the record argument.
    --   Start counting with 1, because 0 means that
    --   it is already applied to the record value.
    --   This can happen in module instantiation, but
    --   then either the record value is @var 0@, or @funProjection == Nothing@.
  , projLams :: ProjLams
    -- ^ Term @t@ to be be applied to record parameters and record value.
    --   The parameters will be dropped.
    --   In case of a proper projection, a postfix projection application
    --   will be created: @t = \ pars r -> r .p@
    --   (Invariant: the number of abstractions equals 'projIndex'.)
    --   In case of a projection-like function, just the function symbol
    --   is returned as 'Def':  @t = \ pars -> f@.
  } deriving (Data, Show)

-- | Abstractions to build projection function (dropping parameters).
newtype ProjLams = ProjLams { getProjLams :: [Arg ArgName] }
  deriving (Data, Show, Null)

-- | Building the projection function (which drops the parameters).
projDropPars :: Projection -> ProjOrigin -> Term
-- Proper projections:
projDropPars (Projection Just{} d _ _ lams) o =
  case initLast $ getProjLams lams of
    Nothing -> Def d []
    Just (pars, Arg i y) ->
      let core = Lam i $ Abs y $ Var 0 [Proj o d] in
      List.foldr (\ (Arg ai x) -> Lam ai . NoAbs x) core pars
-- Projection-like functions:
projDropPars (Projection Nothing _ _ _ lams) o | null lams = __IMPOSSIBLE__
projDropPars (Projection Nothing d _ _ lams) o =
  List.foldr (\ (Arg ai x) -> Lam ai . NoAbs x) (Def d []) $ init $ getProjLams lams

-- | The info of the principal (record) argument.
projArgInfo :: Projection -> ArgInfo
projArgInfo (Projection _ _ _ _ lams) =
  maybe __IMPOSSIBLE__ getArgInfo $ lastMaybe $ getProjLams lams

-- | Should a record type admit eta-equality?
data EtaEquality
  = Specified { theEtaEquality :: !HasEta }  -- ^ User specifed 'eta-equality' or 'no-eta-equality'.
  | Inferred  { theEtaEquality :: !HasEta }  -- ^ Positivity checker inferred whether eta is safe.
  deriving (Data, Show, Eq)

-- | Make sure we do not overwrite a user specification.
setEtaEquality :: EtaEquality -> HasEta -> EtaEquality
setEtaEquality e@Specified{} _ = e
setEtaEquality _ b = Inferred b

data FunctionFlag
  = FunStatic  -- ^ Should calls to this function be normalised at compile-time?
  | FunInline  -- ^ Should calls to this function be inlined by the compiler?
  | FunMacro   -- ^ Is this function a macro?
  deriving (Data, Eq, Ord, Enum, Show)

data CompKit = CompKit
  { nameOfHComp :: Maybe QName
  , nameOfTransp :: Maybe QName
  }
  deriving (Data, Eq, Ord, Show)

emptyCompKit :: CompKit
emptyCompKit = CompKit Nothing Nothing

data Defn = Axiom -- ^ Postulate
          | DataOrRecSig
            { datarecPars :: Int }
            -- ^ Data or record type signature that doesn't yet have a definition
          | GeneralizableVar -- ^ Generalizable variable (introduced in `generalize` block)
          | AbstractDefn Defn
            -- ^ Returned by 'getConstInfo' if definition is abstract.
          | Function
            { funClauses        :: [Clause]
            , funCompiled       :: Maybe CompiledClauses
              -- ^ 'Nothing' while function is still type-checked.
              --   @Just cc@ after type and coverage checking and
              --   translation to case trees.
            , funSplitTree      :: Maybe SplitTree
              -- ^ The split tree constructed by the coverage
              --   checker. Needed to re-compile the clauses after
              --   forcing translation.
            , funTreeless       :: Maybe Compiled
              -- ^ Intermediate representation for compiler backends.
            , funCovering :: [Closure Clause]
              -- ^ Covering clauses computed by coverage checking.
              --   Erased by (IApply) confluence checking(?)
            , funInv            :: FunctionInverse
            , funMutual         :: Maybe [QName]
              -- ^ Mutually recursive functions, @data@s and @record@s.
              --   Does include this function.
              --   Empty list if not recursive.
              --   @Nothing@ if not yet computed (by positivity checker).
            , funAbstr          :: IsAbstract
            , funDelayed        :: Delayed
              -- ^ Are the clauses of this definition delayed?
            , funProjection     :: Maybe Projection
              -- ^ Is it a record projection?
              --   If yes, then return the name of the record type and index of
              --   the record argument.  Start counting with 1, because 0 means that
              --   it is already applied to the record. (Can happen in module
              --   instantiation.) This information is used in the termination
              --   checker.
            , funFlags          :: Set FunctionFlag
            , funTerminates     :: Maybe Bool
              -- ^ Has this function been termination checked?  Did it pass?
            , funExtLam         :: Maybe ExtLamInfo
              -- ^ Is this function generated from an extended lambda?
              --   If yes, then return the number of hidden and non-hidden lambda-lifted arguments
            , funWith           :: Maybe QName
              -- ^ Is this a generated with-function? If yes, then what's the
              --   name of the parent function.
            , funCopatternLHS   :: Bool
              -- ^ Is this a function defined by copatterns?
            }
          | Datatype
            { dataPars           :: Nat            -- ^ Number of parameters.
            , dataIxs            :: Nat            -- ^ Number of indices.
            , dataInduction      :: Induction      -- ^ @data@ or @codata@ (legacy).
            , dataClause         :: (Maybe Clause) -- ^ This might be in an instantiated module.
            , dataCons           :: [QName]
              -- ^ Constructor names , ordered according to the order of their definition.
            , dataSort           :: Sort
            , dataMutual         :: Maybe [QName]
              -- ^ Mutually recursive functions, @data@s and @record@s.
              --   Does include this data type.
              --   Empty if not recursive.
              --   @Nothing@ if not yet computed (by positivity checker).
            , dataAbstr          :: IsAbstract
            , dataPathCons       :: [QName]        -- ^ Path constructor names (subset of dataCons)
            }
          | Record
            { recPars           :: Nat
              -- ^ Number of parameters.
            , recClause         :: Maybe Clause
              -- ^ Was this record type created by a module application?
              --   If yes, the clause is its definition (linking back to the original record type).
            , recConHead        :: ConHead
              -- ^ Constructor name and fields.
            , recNamedCon       :: Bool
              -- ^ Does this record have a @constructor@?
            , recFields         :: [Arg QName]
              -- ^ The record field names.
            , recTel            :: Telescope
              -- ^ The record field telescope. (Includes record parameters.)
              --   Note: @TelV recTel _ == telView' recConType@.
              --   Thus, @recTel@ is redundant.
            , recMutual         :: Maybe [QName]
              -- ^ Mutually recursive functions, @data@s and @record@s.
              --   Does include this record.
              --   Empty if not recursive.
              --   @Nothing@ if not yet computed (by positivity checker).
            , recEtaEquality'    :: EtaEquality
              -- ^ Eta-expand at this record type?
              --   @False@ for unguarded recursive records and coinductive records
              --   unless the user specifies otherwise.
            , recInduction      :: Maybe Induction
              -- ^ 'Inductive' or 'CoInductive'?  Matters only for recursive records.
              --   'Nothing' means that the user did not specify it, which is an error
              --   for recursive records.
            , recAbstr          :: IsAbstract
            , recComp           :: CompKit
            }
          | Constructor
            { conPars   :: Int         -- ^ Number of parameters.
            , conArity  :: Int         -- ^ Number of arguments (excluding parameters).
            , conSrcCon :: ConHead     -- ^ Name of (original) constructor and fields. (This might be in a module instance.)
            , conData   :: QName       -- ^ Name of datatype or record type.
            , conAbstr  :: IsAbstract
            , conInd    :: Induction   -- ^ Inductive or coinductive?
            , conComp   :: (CompKit, Maybe [QName]) -- ^ (cubical composition, projections)
            , conForced :: [IsForced]  -- ^ Which arguments are forced (i.e. determined by the type of the constructor)?
            , conErased :: [Bool]      -- ^ Which arguments are erased at runtime (computed during compilation to treeless)
            }
          | Primitive
            { primAbstr :: IsAbstract
            , primName  :: String
            , primClauses :: [Clause]
              -- ^ 'null' for primitive functions, @not null@ for builtin functions.
            , primInv      :: FunctionInverse
              -- ^ Builtin functions can have inverses. For instance, natural number addition.
            , primCompiled :: Maybe CompiledClauses
              -- ^ 'Nothing' for primitive functions,
              --   @'Just' something@ for builtin functions.
            }
            -- ^ Primitive or builtin functions.
    deriving (Data, Show)

instance Pretty Definition where
  pretty Defn{..} =
    "Defn {" <?> vcat
      [ "defArgInfo        =" <?> pshow defArgInfo
      , "defName           =" <?> pretty defName
      , "defType           =" <?> pretty defType
      , "defPolarity       =" <?> pshow defPolarity
      , "defArgOccurrences =" <?> pshow defArgOccurrences
      , "defGeneralizedParams =" <?> pshow defGeneralizedParams
      , "defDisplay        =" <?> pshow defDisplay -- TODO: pretty DisplayForm
      , "defMutual         =" <?> pshow defMutual
      , "defCompiledRep    =" <?> pshow defCompiledRep
      , "defInstance       =" <?> pshow defInstance
      , "defCopy           =" <?> pshow defCopy
      , "defMatchable      =" <?> pshow defMatchable
      , "defInjective      =" <?> pshow defInjective
      , "theDef            =" <?> pretty theDef ] <+> "}"

instance Pretty Defn where
  pretty Axiom = "Axiom"
  pretty (DataOrRecSig n)   = "DataOrRecSig" <+> pretty n
  pretty GeneralizableVar{} = "GeneralizableVar"
  pretty (AbstractDefn def) = "AbstractDefn" <?> parens (pretty def)
  pretty Function{..} =
    "Function {" <?> vcat
      [ "funClauses      =" <?> vcat (map pretty funClauses)
      , "funCompiled     =" <?> pshow funCompiled
      , "funSplitTree    =" <?> pshow funSplitTree
      , "funTreeless     =" <?> pshow funTreeless
      , "funInv          =" <?> pshow funInv
      , "funMutual       =" <?> pshow funMutual
      , "funAbstr        =" <?> pshow funAbstr
      , "funDelayed      =" <?> pshow funDelayed
      , "funProjection   =" <?> pshow funProjection
      , "funFlags        =" <?> pshow funFlags
      , "funTerminates   =" <?> pshow funTerminates
      , "funWith         =" <?> pshow funWith
      , "funCopatternLHS =" <?> pshow funCopatternLHS ] <?> "}"
  pretty Datatype{..} =
    "Datatype {" <?> vcat
      [ "dataPars       =" <?> pshow dataPars
      , "dataIxs        =" <?> pshow dataIxs
      , "dataInduction  =" <?> pshow dataInduction
      , "dataClause     =" <?> pretty dataClause
      , "dataCons       =" <?> pshow dataCons
      , "dataSort       =" <?> pretty dataSort
      , "dataMutual     =" <?> pshow dataMutual
      , "dataAbstr      =" <?> pshow dataAbstr ] <?> "}"
  pretty Record{..} =
    "Record {" <?> vcat
      [ "recPars         =" <?> pshow recPars
      , "recClause       =" <?> pretty recClause
      , "recConHead      =" <?> pshow recConHead
      , "recNamedCon     =" <?> pshow recNamedCon
      , "recFields       =" <?> pshow recFields
      , "recTel          =" <?> pretty recTel
      , "recMutual       =" <?> pshow recMutual
      , "recEtaEquality' =" <?> pshow recEtaEquality'
      , "recInduction    =" <?> pshow recInduction
      , "recAbstr        =" <?> pshow recAbstr ] <?> "}"
  pretty Constructor{..} =
    "Constructor {" <?> vcat
      [ "conPars   =" <?> pshow conPars
      , "conArity  =" <?> pshow conArity
      , "conSrcCon =" <?> pshow conSrcCon
      , "conData   =" <?> pshow conData
      , "conAbstr  =" <?> pshow conAbstr
      , "conInd    =" <?> pshow conInd
      , "conErased =" <?> pshow conErased ] <?> "}"
  pretty Primitive{..} =
    "Primitive {" <?> vcat
      [ "primAbstr    =" <?> pshow primAbstr
      , "primName     =" <?> pshow primName
      , "primClauses  =" <?> pshow primClauses
      , "primCompiled =" <?> pshow primCompiled ] <?> "}"


-- | Is the record type recursive?
recRecursive :: Defn -> Bool
recRecursive (Record { recMutual = Just qs }) = not $ null qs
recRecursive _ = __IMPOSSIBLE__

recEtaEquality :: Defn -> HasEta
recEtaEquality = theEtaEquality . recEtaEquality'

-- | A template for creating 'Function' definitions, with sensible defaults.
emptyFunction :: Defn
emptyFunction = Function
  { funClauses     = []
  , funCompiled    = Nothing
  , funSplitTree   = Nothing
  , funTreeless    = Nothing
  , funInv         = NotInjective
  , funMutual      = Nothing
  , funAbstr       = ConcreteDef
  , funDelayed     = NotDelayed
  , funProjection  = Nothing
  , funFlags       = Set.empty
  , funTerminates  = Nothing
  , funExtLam      = Nothing
  , funWith        = Nothing
  , funCopatternLHS = False
  , funCovering    = []
  }

funFlag :: FunctionFlag -> Lens' Bool Defn
funFlag flag f def@Function{ funFlags = flags } =
  f (Set.member flag flags) <&>
  \ b -> def{ funFlags = (if b then Set.insert else Set.delete) flag flags }
funFlag _ f def = f False <&> const def

funStatic, funInline, funMacro :: Lens' Bool Defn
funStatic       = funFlag FunStatic
funInline       = funFlag FunInline
funMacro        = funFlag FunMacro

isMacro :: Defn -> Bool
isMacro = (^. funMacro)

-- | Checking whether we are dealing with a function yet to be defined.
isEmptyFunction :: Defn -> Bool
isEmptyFunction def =
  case def of
    Function { funClauses = [] } -> True
    _ -> False

isCopatternLHS :: [Clause] -> Bool
isCopatternLHS = List.any (List.any (isJust . A.isProjP) . namedClausePats)

recCon :: Defn -> QName
recCon Record{ recConHead } = conName recConHead
recCon _ = __IMPOSSIBLE__

defIsRecord :: Defn -> Bool
defIsRecord Record{} = True
defIsRecord _        = False

defIsDataOrRecord :: Defn -> Bool
defIsDataOrRecord Record{}   = True
defIsDataOrRecord Datatype{} = True
defIsDataOrRecord _          = False

defConstructors :: Defn -> [QName]
defConstructors Datatype{dataCons = cs} = cs
defConstructors Record{recConHead = c} = [conName c]
defConstructors _ = __IMPOSSIBLE__

newtype Fields = Fields [(C.Name, Type)]
  deriving Null

-- | Did we encounter a simplifying reduction?
--   In terms of CIC, that would be a iota-reduction.
--   In terms of Agda, this is a constructor or literal
--   pattern that matched.
--   Just beta-reduction (substitution) or delta-reduction
--   (unfolding of definitions) does not count as simplifying?

data Simplification = YesSimplification | NoSimplification
  deriving (Data, Eq, Show)

instance Null Simplification where
  empty = NoSimplification
  null  = (== NoSimplification)

instance Semigroup Simplification where
  YesSimplification <> _ = YesSimplification
  NoSimplification  <> s = s

instance Monoid Simplification where
  mempty = NoSimplification
  mappend = (<>)

data Reduced no yes = NoReduction no | YesReduction Simplification yes
    deriving Functor

-- | Three cases: 1. not reduced, 2. reduced, but blocked, 3. reduced, not blocked.
data IsReduced
  = NotReduced
  | Reduced    (Blocked ())

data MaybeReduced a = MaybeRed
  { isReduced     :: IsReduced
  , ignoreReduced :: a
  }
  deriving (Functor)

instance IsProjElim e => IsProjElim (MaybeReduced e) where
  isProjElim = isProjElim . ignoreReduced

type MaybeReducedArgs = [MaybeReduced (Arg Term)]
type MaybeReducedElims = [MaybeReduced Elim]

notReduced :: a -> MaybeReduced a
notReduced x = MaybeRed NotReduced x

reduced :: Blocked (Arg Term) -> MaybeReduced (Arg Term)
reduced b = case b of
  NotBlocked _ (Arg _ (MetaV x _)) -> MaybeRed (Reduced $ Blocked x ()) v
  _                                -> MaybeRed (Reduced $ () <$ b)      v
  where
    v = ignoreBlocking b

-- | Controlling 'reduce'.
data AllowedReduction
  = ProjectionReductions     -- ^ (Projection and) projection-like functions may be reduced.
  | InlineReductions         -- ^ Functions marked INLINE may be reduced.
  | CopatternReductions      -- ^ Copattern definitions may be reduced.
  | FunctionReductions       -- ^ Non-recursive functions and primitives may be reduced.
  | RecursiveReductions      -- ^ Even recursive functions may be reduced.
  | LevelReductions          -- ^ Reduce @'Level'@ terms.
  | UnconfirmedReductions    -- ^ Functions whose termination has not (yet) been confirmed.
  | NonTerminatingReductions -- ^ Functions that have failed termination checking.
  deriving (Show, Eq, Ord, Enum, Bounded, Data)

type AllowedReductions = [AllowedReduction]

-- | Not quite all reductions (skip non-terminating reductions)
allReductions :: AllowedReductions
allReductions = [minBound..pred maxBound]

data PrimFun = PrimFun
        { primFunName           :: QName
        , primFunArity          :: Arity
        , primFunImplementation :: [Arg Term] -> Int -> ReduceM (Reduced MaybeReducedArgs Term)
        }

primFun :: QName -> Arity -> ([Arg Term] -> ReduceM (Reduced MaybeReducedArgs Term)) -> PrimFun
primFun q ar imp = PrimFun q ar (\ args _ -> imp args)

defClauses :: Definition -> [Clause]
defClauses Defn{theDef = Function{funClauses = cs}}        = cs
defClauses Defn{theDef = Primitive{primClauses = cs}}      = cs
defClauses Defn{theDef = Datatype{dataClause = Just c}}    = [c]
defClauses Defn{theDef = Record{recClause = Just c}}       = [c]
defClauses _                                               = []

defCompiled :: Definition -> Maybe CompiledClauses
defCompiled Defn{theDef = Function {funCompiled  = mcc}} = mcc
defCompiled Defn{theDef = Primitive{primCompiled = mcc}} = mcc
defCompiled _ = Nothing

defParameters :: Definition -> Maybe Nat
defParameters Defn{theDef = Datatype{dataPars = n}} = Just n
defParameters Defn{theDef = Record  {recPars  = n}} = Just n
defParameters _                                     = Nothing

defInverse :: Definition -> FunctionInverse
defInverse Defn{theDef = Function { funInv  = inv }} = inv
defInverse Defn{theDef = Primitive{ primInv = inv }} = inv
defInverse _                                         = NotInjective

defCompilerPragmas :: BackendName -> Definition -> [CompilerPragma]
defCompilerPragmas b = reverse . fromMaybe [] . Map.lookup b . defCompiledRep
  -- reversed because we add new pragmas to the front of the list

-- | Are the clauses of this definition delayed?
defDelayed :: Definition -> Delayed
defDelayed Defn{theDef = Function{funDelayed = d}} = d
defDelayed _                                       = NotDelayed

-- | Has the definition failed the termination checker?
defNonterminating :: Definition -> Bool
defNonterminating Defn{theDef = Function{funTerminates = Just False}} = True
defNonterminating _                                                   = False

-- | Has the definition not termination checked or did the check fail?
defTerminationUnconfirmed :: Definition -> Bool
defTerminationUnconfirmed Defn{theDef = Function{funTerminates = Just True}} = False
defTerminationUnconfirmed Defn{theDef = Function{funTerminates = _        }} = True
defTerminationUnconfirmed _ = False

defAbstract :: Definition -> IsAbstract
defAbstract d = case theDef d of
    Axiom{}                   -> ConcreteDef
    DataOrRecSig{}            -> ConcreteDef
    GeneralizableVar{}        -> ConcreteDef
    AbstractDefn{}            -> AbstractDef
    Function{funAbstr = a}    -> a
    Datatype{dataAbstr = a}   -> a
    Record{recAbstr = a}      -> a
    Constructor{conAbstr = a} -> a
    Primitive{primAbstr = a}  -> a

defForced :: Definition -> [IsForced]
defForced d = case theDef d of
    Constructor{conForced = fs} -> fs
    Axiom{}                     -> []
    DataOrRecSig{}              -> []
    GeneralizableVar{}          -> []
    AbstractDefn{}              -> []
    Function{}                  -> []
    Datatype{}                  -> []
    Record{}                    -> []
    Primitive{}                 -> []

---------------------------------------------------------------------------
-- ** Injectivity
---------------------------------------------------------------------------

type FunctionInverse = FunctionInverse' Clause
type InversionMap c = Map TermHead [c]

data FunctionInverse' c
  = NotInjective
  | Inverse (InversionMap c)
  deriving (Data, Show, Functor)

data TermHead = SortHead
              | PiHead
              | ConsHead QName
              | VarHead Nat
              | UnknownHead
  deriving (Data, Eq, Ord, Show)

instance Pretty TermHead where
  pretty = \ case
    SortHead    -> "SortHead"
    PiHead      -> "PiHead"
    ConsHead q  -> "ConsHead" <+> pretty q
    VarHead i   -> text ("VarHead " ++ show i)
    UnknownHead -> "UnknownHead"

---------------------------------------------------------------------------
-- ** Mutual blocks
---------------------------------------------------------------------------

newtype MutualId = MutId Int32
  deriving (Data, Eq, Ord, Show, Num, Enum)

---------------------------------------------------------------------------
-- ** Statistics
---------------------------------------------------------------------------

type Statistics = Map String Integer

---------------------------------------------------------------------------
-- ** Trace
---------------------------------------------------------------------------

data Call = CheckClause Type A.SpineClause
          | CheckPattern A.Pattern Telescope Type
          | CheckLetBinding A.LetBinding
          | InferExpr A.Expr
          | CheckExprCall Comparison A.Expr Type
          | CheckDotPattern A.Expr Term
          | CheckPatternShadowing A.SpineClause
          | CheckProjection Range QName Type
          | IsTypeCall A.Expr Sort
          | IsType_ A.Expr
          | InferVar Name
          | InferDef QName
          | CheckArguments Range [NamedArg A.Expr] Type (Maybe Type)
          | CheckTargetType Range Type Type
          | CheckDataDef Range QName [A.LamBinding] [A.Constructor]
          | CheckRecDef Range QName [A.LamBinding] [A.Constructor]
          | CheckConstructor QName Telescope Sort A.Constructor
          | CheckConstructorFitsIn QName Type Sort
          | CheckFunDefCall Range QName [A.Clause]
          | CheckPragma Range A.Pragma
          | CheckPrimitive Range QName A.Expr
          | CheckIsEmpty Range Type
          | CheckWithFunctionType Type
          | CheckSectionApplication Range ModuleName A.ModuleApplication
          | CheckNamedWhere ModuleName
          | ScopeCheckExpr C.Expr
          | ScopeCheckDeclaration NiceDeclaration
          | ScopeCheckLHS C.QName C.Pattern
          | NoHighlighting
          | ModuleContents  -- ^ Interaction command: show module contents.
          | SetRange Range  -- ^ used by 'setCurrentRange'
    deriving Data

instance Pretty Call where
    pretty CheckClause{}             = "CheckClause"
    pretty CheckPattern{}            = "CheckPattern"
    pretty InferExpr{}               = "InferExpr"
    pretty CheckExprCall{}           = "CheckExprCall"
    pretty CheckLetBinding{}         = "CheckLetBinding"
    pretty CheckProjection{}         = "CheckProjection"
    pretty IsTypeCall{}              = "IsTypeCall"
    pretty IsType_{}                 = "IsType_"
    pretty InferVar{}                = "InferVar"
    pretty InferDef{}                = "InferDef"
    pretty CheckArguments{}          = "CheckArguments"
    pretty CheckTargetType{}         = "CheckTargetType"
    pretty CheckDataDef{}            = "CheckDataDef"
    pretty CheckRecDef{}             = "CheckRecDef"
    pretty CheckConstructor{}        = "CheckConstructor"
    pretty CheckConstructorFitsIn{}  = "CheckConstructorFitsIn"
    pretty CheckFunDefCall{}         = "CheckFunDefCall"
    pretty CheckPragma{}             = "CheckPragma"
    pretty CheckPrimitive{}          = "CheckPrimitive"
    pretty CheckWithFunctionType{}   = "CheckWithFunctionType"
    pretty CheckNamedWhere{}         = "CheckNamedWhere"
    pretty ScopeCheckExpr{}          = "ScopeCheckExpr"
    pretty ScopeCheckDeclaration{}   = "ScopeCheckDeclaration"
    pretty ScopeCheckLHS{}           = "ScopeCheckLHS"
    pretty CheckDotPattern{}         = "CheckDotPattern"
    pretty CheckPatternShadowing{}   = "CheckPatternShadowing"
    pretty SetRange{}                = "SetRange"
    pretty CheckSectionApplication{} = "CheckSectionApplication"
    pretty CheckIsEmpty{}            = "CheckIsEmpty"
    pretty NoHighlighting{}          = "NoHighlighting"
    pretty ModuleContents{}          = "ModuleContents"

instance HasRange Call where
    getRange (CheckClause _ c)               = getRange c
    getRange (CheckPattern p _ _)            = getRange p
    getRange (InferExpr e)                   = getRange e
    getRange (CheckExprCall _ e _)           = getRange e
    getRange (CheckLetBinding b)             = getRange b
    getRange (CheckProjection r _ _)         = r
    getRange (IsTypeCall e s)                = getRange e
    getRange (IsType_ e)                     = getRange e
    getRange (InferVar x)                    = getRange x
    getRange (InferDef f)                    = getRange f
    getRange (CheckArguments r _ _ _)        = r
    getRange (CheckTargetType r _ _)         = r
    getRange (CheckDataDef i _ _ _)          = getRange i
    getRange (CheckRecDef i _ _ _)           = getRange i
    getRange (CheckConstructor _ _ _ c)      = getRange c
    getRange (CheckConstructorFitsIn c _ _)  = getRange c
    getRange (CheckFunDefCall i _ _)         = getRange i
    getRange (CheckPragma r _)               = r
    getRange (CheckPrimitive i _ _)          = getRange i
    getRange CheckWithFunctionType{}         = noRange
    getRange (CheckNamedWhere m)             = getRange m
    getRange (ScopeCheckExpr e)              = getRange e
    getRange (ScopeCheckDeclaration d)       = getRange d
    getRange (ScopeCheckLHS _ p)             = getRange p
    getRange (CheckDotPattern e _)           = getRange e
    getRange (CheckPatternShadowing c)       = getRange c
    getRange (SetRange r)                    = r
    getRange (CheckSectionApplication r _ _) = r
    getRange (CheckIsEmpty r _)              = r
    getRange NoHighlighting                  = noRange
    getRange ModuleContents                  = noRange

---------------------------------------------------------------------------
-- ** Instance table
---------------------------------------------------------------------------

-- | The instance table is a @Map@ associating to every name of
--   record/data type/postulate its list of instances
type InstanceTable = Map QName (Set QName)

-- | When typechecking something of the following form:
--
--     instance
--       x : _
--       x = y
--
--   it's not yet known where to add @x@, so we add it to a list of
--   unresolved instances and we'll deal with it later.
type TempInstanceTable = (InstanceTable , Set QName)

---------------------------------------------------------------------------
-- ** Builtin things
---------------------------------------------------------------------------

data BuiltinDescriptor
  = BuiltinData (TCM Type) [String]
  | BuiltinDataCons (TCM Type)
  | BuiltinPrim String (Term -> TCM ())
  | BuiltinPostulate Relevance (TCM Type)
  | BuiltinUnknown (Maybe (TCM Type)) (Term -> Type -> TCM ())
    -- ^ Builtin of any kind.
    --   Type can be checked (@Just t@) or inferred (@Nothing@).
    --   The second argument is the hook for the verification function.

data BuiltinInfo =
   BuiltinInfo { builtinName :: String
               , builtinDesc :: BuiltinDescriptor }

type BuiltinThings pf = Map String (Builtin pf)

data Builtin pf
        = Builtin Term
        | Prim pf
    deriving (Show, Functor, Foldable, Traversable)

---------------------------------------------------------------------------
-- * Highlighting levels
---------------------------------------------------------------------------

-- | How much highlighting should be sent to the user interface?

data HighlightingLevel
  = None
  | NonInteractive
  | Interactive
    -- ^ This includes both non-interactive highlighting and
    -- interactive highlighting of the expression that is currently
    -- being type-checked.
    deriving (Eq, Ord, Show, Read, Data)

-- | How should highlighting be sent to the user interface?

data HighlightingMethod
  = Direct
    -- ^ Via stdout.
  | Indirect
    -- ^ Both via files and via stdout.
    deriving (Eq, Show, Read, Data)

-- | @ifTopLevelAndHighlightingLevelIs l b m@ runs @m@ when we're
-- type-checking the top-level module and either the highlighting
-- level is /at least/ @l@ or @b@ is 'True'.

ifTopLevelAndHighlightingLevelIsOr ::
  MonadTCM tcm => HighlightingLevel -> Bool -> tcm () -> tcm ()
ifTopLevelAndHighlightingLevelIsOr l b m = do
  e <- askTC
  when (envModuleNestingLevel e == 0 &&
        (envHighlightingLevel e >= l || b))
       m

-- | @ifTopLevelAndHighlightingLevelIs l m@ runs @m@ when we're
-- type-checking the top-level module and the highlighting level is
-- /at least/ @l@.

ifTopLevelAndHighlightingLevelIs ::
  MonadTCM tcm => HighlightingLevel -> tcm () -> tcm ()
ifTopLevelAndHighlightingLevelIs l =
  ifTopLevelAndHighlightingLevelIsOr l False

---------------------------------------------------------------------------
-- * Type checking environment
---------------------------------------------------------------------------

data TCEnv =
    TCEnv { envContext             :: Context
          , envLetBindings         :: LetBindings
          , envCurrentModule       :: ModuleName
          , envCurrentPath         :: Maybe AbsolutePath
            -- ^ The path to the file that is currently being
            -- type-checked.  'Nothing' if we do not have a file
            -- (like in interactive mode see @CommandLine@).
          , envAnonymousModules    :: [(ModuleName, Nat)] -- ^ anonymous modules and their number of free variables
          , envImportPath          :: [C.TopLevelModuleName] -- ^ to detect import cycles
          , envMutualBlock         :: Maybe MutualId -- ^ the current (if any) mutual block
          , envTerminationCheck    :: TerminationCheck ()  -- ^ are we inside the scope of a termination pragma
          , envSolvingConstraints  :: Bool
                -- ^ Are we currently in the process of solving active constraints?
          , envCheckingWhere       :: Bool
                -- ^ Have we stepped into the where-declarations of a clause?
                --   Everything under a @where@ will be checked with this flag on.
          , envWorkingOnTypes      :: Bool
                -- ^ Are we working on types? Turned on by 'workOnTypes'.
          , envAssignMetas         :: Bool
            -- ^ Are we allowed to assign metas?
          , envActiveProblems      :: Set ProblemId
          , envAbstractMode        :: AbstractMode
                -- ^ When checking the typesignature of a public definition
                --   or the body of a non-abstract definition this is true.
                --   To prevent information about abstract things leaking
                --   outside the module.
          , envModality            :: Modality
                -- ^ 'Relevance' component:
                -- Are we checking an irrelevant argument? (=@Irrelevant@)
                -- Then top-level irrelevant declarations are enabled.
                -- Other value: @Relevant@, then only relevant decls. are available.
                --
                -- 'Quantity' component:
                -- Are we checking a runtime-irrelevant thing? (='Quantity0')
                -- Then runtime-irrelevant things are usable.
                -- Other value: @Quantity1@, runtime relevant.
                -- @Quantityω@ is not allowed here, see Bob Atkey, LiCS 2018.
          , envDisplayFormsEnabled :: Bool
                -- ^ Sometimes we want to disable display forms.
          , envRange :: Range
          , envHighlightingRange :: Range
                -- ^ Interactive highlighting uses this range rather
                --   than 'envRange'.
          , envClause :: IPClause
                -- ^ What is the current clause we are type-checking?
                --   Will be recorded in interaction points in this clause.
          , envCall  :: Maybe (Closure Call)
                -- ^ what we're doing at the moment
          , envHighlightingLevel  :: HighlightingLevel
                -- ^ Set to 'None' when imported modules are
                --   type-checked.
          , envHighlightingMethod :: HighlightingMethod
          , envModuleNestingLevel :: !Int
                -- ^ This number indicates how far away from the
                --   top-level module Agda has come when chasing
                --   modules. The level of a given module is not
                --   necessarily the same as the length, in the module
                --   dependency graph, of the shortest path from the
                --   top-level module; it depends on in which order
                --   Agda chooses to chase dependencies.
          , envExpandLast :: ExpandHidden
                -- ^ When type-checking an alias f=e, we do not want
                -- to insert hidden arguments in the end, because
                -- these will become unsolved metas.
          , envAppDef :: Maybe QName
                -- ^ We are reducing an application of this function.
                -- (For debugging of incomplete matches only.)
          , envSimplification :: Simplification
                -- ^ Did we encounter a simplification (proper match)
                --   during the current reduction process?
          , envAllowedReductions :: AllowedReductions
          , envInjectivityDepth :: Int
                -- ^ Injectivity can cause non-termination for unsolvable contraints
                --   (#431, #3067). Keep a limit on the nesting depth of injectivity
                --   uses.
          , envCompareBlocked :: Bool
                -- ^ Can we compare blocked things during conversion?
                --   No by default.
                --   Yes for rewriting feature.
          , envPrintDomainFreePi :: Bool
                -- ^ When @True@, types will be omitted from printed pi types if they
                --   can be inferred.
          , envPrintMetasBare :: Bool
                -- ^ When @True@, throw away meta numbers and meta elims.
                --   This is used for reifying terms for feeding into the
                --   user's source code, e.g., for the interaction tactics @solveAll@.
          , envInsideDotPattern :: Bool
                -- ^ Used by the scope checker to make sure that certain forms
                --   of expressions are not used inside dot patterns: extended
                --   lambdas and let-expressions.
          , envUnquoteFlags :: UnquoteFlags
          , envInstanceDepth :: !Int
                -- ^ Until we get a termination checker for instance search (#1743) we
                --   limit the search depth to ensure termination.
          , envIsDebugPrinting :: Bool
          , envPrintingPatternLambdas :: [QName]
                -- ^ #3004: pattern lambdas with copatterns may refer to themselves. We
                --   don't have a good story for what to do in this case, but at least
                --   printing shouldn't loop. Here we keep track of which pattern lambdas
                --   we are currently in the process of printing.
          , envCallByNeed :: Bool
                -- ^ Use call-by-need evaluation for reductions.
          , envCurrentCheckpoint :: CheckpointId
                -- ^ Checkpoints track the evolution of the context as we go
                -- under binders or refine it by pattern matching.
          , envCheckpoints :: Map CheckpointId Substitution
                -- ^ Keeps the substitution from each previous checkpoint to
                --   the current context.
          , envGeneralizeMetas :: DoGeneralize
                -- ^ Should new metas generalized over.
          , envGeneralizedVars :: Map QName GeneralizedValue
                -- ^ Values for used generalizable variables.
          , envCheckOptionConsistency :: Bool
                -- ^ Do we check that options in imported files are
                --   consistent with each other?
          }
    deriving Data

initEnv :: TCEnv
initEnv = TCEnv { envContext             = []
                , envLetBindings         = Map.empty
                , envCurrentModule       = noModuleName
                , envCurrentPath         = Nothing
                , envAnonymousModules    = []
                , envImportPath          = []
                , envMutualBlock         = Nothing
                , envTerminationCheck    = TerminationCheck
                , envSolvingConstraints  = False
                , envCheckingWhere       = False
                , envActiveProblems      = Set.empty
                , envWorkingOnTypes      = False
                , envAssignMetas         = True
                , envAbstractMode        = ConcreteMode
  -- Andreas, 2013-02-21:  This was 'AbstractMode' until now.
  -- However, top-level checks for mutual blocks, such as
  -- constructor-headedness, should not be able to look into
  -- abstract definitions unless abstract themselves.
  -- (See also discussion on issue 796.)
  -- The initial mode should be 'ConcreteMode', ensuring you
  -- can only look into abstract things in an abstract
  -- definition (which sets 'AbstractMode').
                , envModality               = Modality Relevant Quantity1
                , envDisplayFormsEnabled    = True
                , envRange                  = noRange
                , envHighlightingRange      = noRange
                , envClause                 = IPNoClause
                , envCall                   = Nothing
                , envHighlightingLevel      = None
                , envHighlightingMethod     = Indirect
                , envModuleNestingLevel     = -1
                , envExpandLast             = ExpandLast
                , envAppDef                 = Nothing
                , envSimplification         = NoSimplification
                , envAllowedReductions      = allReductions
                , envInjectivityDepth       = 0
                , envCompareBlocked         = False
                , envPrintDomainFreePi      = False
                , envPrintMetasBare         = False
                , envInsideDotPattern       = False
                , envUnquoteFlags           = defaultUnquoteFlags
                , envInstanceDepth          = 0
                , envIsDebugPrinting        = False
                , envPrintingPatternLambdas = []
                , envCallByNeed             = True
                , envCurrentCheckpoint      = 0
                , envCheckpoints            = Map.singleton 0 IdS
                , envGeneralizeMetas        = NoGeneralize
                , envGeneralizedVars        = Map.empty
                , envCheckOptionConsistency = True
                }

-- | Project 'Relevance' component of 'TCEnv'.
envRelevance :: TCEnv -> Relevance
envRelevance = modRelevance . envModality

data UnquoteFlags = UnquoteFlags
  { _unquoteNormalise :: Bool }
  deriving Data

defaultUnquoteFlags :: UnquoteFlags
defaultUnquoteFlags = UnquoteFlags
  { _unquoteNormalise = False }

unquoteNormalise :: Lens' Bool UnquoteFlags
unquoteNormalise f e = f (_unquoteNormalise e) <&> \ x -> e { _unquoteNormalise = x }

eUnquoteNormalise :: Lens' Bool TCEnv
eUnquoteNormalise = eUnquoteFlags . unquoteNormalise

-- * e-prefixed lenses
------------------------------------------------------------------------

eContext :: Lens' Context TCEnv
eContext f e = f (envContext e) <&> \ x -> e { envContext = x }

eLetBindings :: Lens' LetBindings TCEnv
eLetBindings f e = f (envLetBindings e) <&> \ x -> e { envLetBindings = x }

eCurrentModule :: Lens' ModuleName TCEnv
eCurrentModule f e = f (envCurrentModule e) <&> \ x -> e { envCurrentModule = x }

eCurrentPath :: Lens' (Maybe AbsolutePath) TCEnv
eCurrentPath f e = f (envCurrentPath e) <&> \ x -> e { envCurrentPath = x }

eAnonymousModules :: Lens' [(ModuleName, Nat)] TCEnv
eAnonymousModules f e = f (envAnonymousModules e) <&> \ x -> e { envAnonymousModules = x }

eImportPath :: Lens' [C.TopLevelModuleName] TCEnv
eImportPath f e = f (envImportPath e) <&> \ x -> e { envImportPath = x }

eMutualBlock :: Lens' (Maybe MutualId) TCEnv
eMutualBlock f e = f (envMutualBlock e) <&> \ x -> e { envMutualBlock = x }

eTerminationCheck :: Lens' (TerminationCheck ()) TCEnv
eTerminationCheck f e = f (envTerminationCheck e) <&> \ x -> e { envTerminationCheck = x }

eSolvingConstraints :: Lens' Bool TCEnv
eSolvingConstraints f e = f (envSolvingConstraints e) <&> \ x -> e { envSolvingConstraints = x }

eCheckingWhere :: Lens' Bool TCEnv
eCheckingWhere f e = f (envCheckingWhere e) <&> \ x -> e { envCheckingWhere = x }

eWorkingOnTypes :: Lens' Bool TCEnv
eWorkingOnTypes f e = f (envWorkingOnTypes e) <&> \ x -> e { envWorkingOnTypes = x }

eAssignMetas :: Lens' Bool TCEnv
eAssignMetas f e = f (envAssignMetas e) <&> \ x -> e { envAssignMetas = x }

eActiveProblems :: Lens' (Set ProblemId) TCEnv
eActiveProblems f e = f (envActiveProblems e) <&> \ x -> e { envActiveProblems = x }

eAbstractMode :: Lens' AbstractMode TCEnv
eAbstractMode f e = f (envAbstractMode e) <&> \ x -> e { envAbstractMode = x }

eModality :: Lens' Modality TCEnv
eModality f e = f (envModality e) <&> \ x -> e { envModality = x }

eRelevance :: Lens' Relevance TCEnv
eRelevance = eModality . lModRelevance

eQuantity :: Lens' Quantity TCEnv
eQuantity = eModality . lModQuantity

eDisplayFormsEnabled :: Lens' Bool TCEnv
eDisplayFormsEnabled f e = f (envDisplayFormsEnabled e) <&> \ x -> e { envDisplayFormsEnabled = x }

eRange :: Lens' Range TCEnv
eRange f e = f (envRange e) <&> \ x -> e { envRange = x }

eHighlightingRange :: Lens' Range TCEnv
eHighlightingRange f e = f (envHighlightingRange e) <&> \ x -> e { envHighlightingRange = x }

eCall :: Lens' (Maybe (Closure Call)) TCEnv
eCall f e = f (envCall e) <&> \ x -> e { envCall = x }

eHighlightingLevel :: Lens' HighlightingLevel TCEnv
eHighlightingLevel f e = f (envHighlightingLevel e) <&> \ x -> e { envHighlightingLevel = x }

eHighlightingMethod :: Lens' HighlightingMethod TCEnv
eHighlightingMethod f e = f (envHighlightingMethod e) <&> \ x -> e { envHighlightingMethod = x }

eModuleNestingLevel :: Lens' Int TCEnv
eModuleNestingLevel f e = f (envModuleNestingLevel e) <&> \ x -> e { envModuleNestingLevel = x }

eExpandLast :: Lens' ExpandHidden TCEnv
eExpandLast f e = f (envExpandLast e) <&> \ x -> e { envExpandLast = x }

eAppDef :: Lens' (Maybe QName) TCEnv
eAppDef f e = f (envAppDef e) <&> \ x -> e { envAppDef = x }

eSimplification :: Lens' Simplification TCEnv
eSimplification f e = f (envSimplification e) <&> \ x -> e { envSimplification = x }

eAllowedReductions :: Lens' AllowedReductions TCEnv
eAllowedReductions f e = f (envAllowedReductions e) <&> \ x -> e { envAllowedReductions = x }

eInjectivityDepth :: Lens' Int TCEnv
eInjectivityDepth f e = f (envInjectivityDepth e) <&> \ x -> e { envInjectivityDepth = x }

eCompareBlocked :: Lens' Bool TCEnv
eCompareBlocked f e = f (envCompareBlocked e) <&> \ x -> e { envCompareBlocked = x }

ePrintDomainFreePi :: Lens' Bool TCEnv
ePrintDomainFreePi f e = f (envPrintDomainFreePi e) <&> \ x -> e { envPrintDomainFreePi = x }

eInsideDotPattern :: Lens' Bool TCEnv
eInsideDotPattern f e = f (envInsideDotPattern e) <&> \ x -> e { envInsideDotPattern = x }

eUnquoteFlags :: Lens' UnquoteFlags TCEnv
eUnquoteFlags f e = f (envUnquoteFlags e) <&> \ x -> e { envUnquoteFlags = x }

eInstanceDepth :: Lens' Int TCEnv
eInstanceDepth f e = f (envInstanceDepth e) <&> \ x -> e { envInstanceDepth = x }

eIsDebugPrinting :: Lens' Bool TCEnv
eIsDebugPrinting f e = f (envIsDebugPrinting e) <&> \ x -> e { envIsDebugPrinting = x }

ePrintingPatternLambdas :: Lens' [QName] TCEnv
ePrintingPatternLambdas f e = f (envPrintingPatternLambdas e) <&> \ x -> e { envPrintingPatternLambdas = x }

eCallByNeed :: Lens' Bool TCEnv
eCallByNeed f e = f (envCallByNeed e) <&> \ x -> e { envCallByNeed = x }

eCurrentCheckpoint :: Lens' CheckpointId TCEnv
eCurrentCheckpoint f e = f (envCurrentCheckpoint e) <&> \ x -> e { envCurrentCheckpoint = x }

eCheckpoints :: Lens' (Map CheckpointId Substitution) TCEnv
eCheckpoints f e = f (envCheckpoints e) <&> \ x -> e { envCheckpoints = x }

eGeneralizeMetas :: Lens' DoGeneralize TCEnv
eGeneralizeMetas f e = f (envGeneralizeMetas e) <&> \ x -> e { envGeneralizeMetas = x }

eGeneralizedVars :: Lens' (Map QName GeneralizedValue) TCEnv
eGeneralizedVars f e = f (envGeneralizedVars e) <&> \ x -> e { envGeneralizedVars = x }

---------------------------------------------------------------------------
-- ** Context
---------------------------------------------------------------------------

-- | The @Context@ is a stack of 'ContextEntry's.
type Context      = [ContextEntry]
type ContextEntry = Dom (Name, Type)

---------------------------------------------------------------------------
-- ** Let bindings
---------------------------------------------------------------------------

type LetBindings = Map Name (Open (Term, Dom Type))

---------------------------------------------------------------------------
-- ** Abstract mode
---------------------------------------------------------------------------

data AbstractMode
  = AbstractMode        -- ^ Abstract things in the current module can be accessed.
  | ConcreteMode        -- ^ No abstract things can be accessed.
  | IgnoreAbstractMode  -- ^ All abstract things can be accessed.
  deriving (Data, Show, Eq)

aDefToMode :: IsAbstract -> AbstractMode
aDefToMode AbstractDef = AbstractMode
aDefToMode ConcreteDef = ConcreteMode

aModeToDef :: AbstractMode -> IsAbstract
aModeToDef AbstractMode = AbstractDef
aModeToDef ConcreteMode = ConcreteDef
aModeToDef _ = __IMPOSSIBLE__

---------------------------------------------------------------------------
-- ** Insertion of implicit arguments
---------------------------------------------------------------------------

data ExpandHidden
  = ExpandLast      -- ^ Add implicit arguments in the end until type is no longer hidden 'Pi'.
  | DontExpandLast  -- ^ Do not append implicit arguments.
  deriving (Eq, Data)

-- | A candidate solution for an instance meta is a term with its type.
--   It may be the case that the candidate is not fully applied yet or
--   of the wrong type, hence the need for the type.
data Candidate  = Candidate { candidateTerm :: Term
                            , candidateType :: Type
                            , candidateOverlappable :: Bool
                            }
  deriving (Show, Data)

instance Free Candidate where
  freeVars' (Candidate t u _) = freeVars' (t, u)

---------------------------------------------------------------------------
-- * Type checking warnings (aka non-fatal errors)
---------------------------------------------------------------------------

-- | A non-fatal error is an error which does not prevent us from
-- checking the document further and interacting with the user.

data Warning
  = NicifierIssue            DeclarationWarning
  | TerminationIssue         [TerminationError]
  | UnreachableClauses       QName [[NamedArg DeBruijnPattern]]
  | CoverageIssue            QName [(Telescope, [NamedArg DeBruijnPattern])]
  -- ^ `CoverageIssue f pss` means that `pss` are not covered in `f`
  | CoverageNoExactSplit     QName [Clause]
  | NotStrictlyPositive      QName (Seq OccursWhere)
  | UnsolvedMetaVariables    [Range]  -- ^ Do not use directly with 'warning'
  | UnsolvedInteractionMetas [Range]  -- ^ Do not use directly with 'warning'
  | UnsolvedConstraints      Constraints
    -- ^ Do not use directly with 'warning'
  | CantGeneralizeOverSorts [MetaId]
  | AbsurdPatternRequiresNoRHS [NamedArg DeBruijnPattern]
  | OldBuiltin               String String
    -- ^ In `OldBuiltin old new`, the BUILTIN old has been replaced by new
  | EmptyRewritePragma
    -- ^ If the user wrote just @{-\# REWRITE \#-}@.
  | IllformedAsClause String
    -- ^ If the user wrote something other than an unqualified name
    --   in the @as@ clause of an @import@ statement.
    --   The 'String' gives optionally extra explanation.
  | UselessPublic
    -- ^ If the user opens a module public before the module header.
    --   (See issue #2377.)
  | UselessInline            QName
  | WrongInstanceDeclaration
  | InstanceWithExplicitArg  QName
  -- ^ An instance was declared with an implicit argument, which means it
  --   will never actually be considered by instance search.
  | InstanceNoOutputTypeName Doc
  -- ^ The type of an instance argument doesn't end in a named or
  -- variable type, so it will never be considered by instance search.
  | InstanceArgWithExplicitArg Doc
  -- ^ As InstanceWithExplicitArg, but for local bindings rather than
  --   top-level instances.
  | InversionDepthReached    QName
  -- ^ The --inversion-max-depth was reached.
  -- Generic warnings for one-off things
  | GenericWarning           Doc
    -- ^ Harmless generic warning (not an error)
  | GenericNonFatalError     Doc
    -- ^ Generic error which doesn't abort proceedings (not a warning)
  -- Safe flag errors
  | SafeFlagPostulate C.Name
  | SafeFlagPragma [String]
  | SafeFlagNonTerminating
  | SafeFlagTerminating
  | SafeFlagWithoutKFlagPrimEraseEquality
  | WithoutKFlagPrimEraseEquality
  | SafeFlagNoPositivityCheck
  | SafeFlagPolarity
  | SafeFlagNoUniverseCheck
  | ParseWarning             ParseWarning
  | LibraryWarning           LibWarning
  | DeprecationWarning String String String
    -- ^ `DeprecationWarning old new version`:
    --   `old` is deprecated, use `new` instead. This will be an error in Agda `version`.
  | UserWarning String
    -- ^ User-defined warning (e.g. to mention that a name is deprecated)
  | ModuleDoesntExport C.QName [C.ImportedName]
    -- ^ Some imported names are not actually exported by the source module
  | InfectiveImport String ModuleName
    -- ^ Importing a file using an infective option into one which doesn't
  | CoInfectiveImport String ModuleName
    -- ^ Importing a file not using a coinfective option from one which does
  deriving (Show , Data)


warningName :: Warning -> WarningName
warningName w = case w of
  -- special cases
  NicifierIssue dw             -> declarationWarningName dw
  ParseWarning pw              -> parseWarningName pw
  LibraryWarning lw            -> libraryWarningName lw
  -- typechecking errors
  CantGeneralizeOverSorts{}    -> CantGeneralizeOverSorts_
  AbsurdPatternRequiresNoRHS{} -> AbsurdPatternRequiresNoRHS_
  CoverageIssue{}              -> CoverageIssue_
  CoverageNoExactSplit{}       -> CoverageNoExactSplit_
  DeprecationWarning{}         -> DeprecationWarning_
  EmptyRewritePragma           -> EmptyRewritePragma_
  IllformedAsClause{}          -> IllformedAsClause_
  WrongInstanceDeclaration{}   -> WrongInstanceDeclaration_
  InstanceWithExplicitArg{}    -> InstanceWithExplicitArg_
  InstanceNoOutputTypeName{}   -> InstanceNoOutputTypeName_
  InstanceArgWithExplicitArg{} -> InstanceArgWithExplicitArg_
  GenericNonFatalError{}       -> GenericNonFatalError_
  GenericWarning{}             -> GenericWarning_
  InversionDepthReached{}      -> InversionDepthReached_
  ModuleDoesntExport{}         -> ModuleDoesntExport_
  NotStrictlyPositive{}        -> NotStrictlyPositive_
  OldBuiltin{}                 -> OldBuiltin_
  SafeFlagNoPositivityCheck    -> SafeFlagNoPositivityCheck_
  SafeFlagNonTerminating       -> SafeFlagNonTerminating_
  SafeFlagNoUniverseCheck      -> SafeFlagNoUniverseCheck_
  SafeFlagPolarity             -> SafeFlagPolarity_
  SafeFlagPostulate{}          -> SafeFlagPostulate_
  SafeFlagPragma{}             -> SafeFlagPragma_
  SafeFlagWithoutKFlagPrimEraseEquality -> SafeFlagWithoutKFlagPrimEraseEquality_
  WithoutKFlagPrimEraseEquality -> WithoutKFlagPrimEraseEquality_
  SafeFlagTerminating          -> SafeFlagTerminating_
  TerminationIssue{}           -> TerminationIssue_
  UnreachableClauses{}         -> UnreachableClauses_
  UnsolvedInteractionMetas{}   -> UnsolvedInteractionMetas_
  UnsolvedConstraints{}        -> UnsolvedConstraints_
  UnsolvedMetaVariables{}      -> UnsolvedMetaVariables_
  UselessInline{}              -> UselessInline_
  UselessPublic                -> UselessPublic_
  UserWarning{}                -> UserWarning_
  InfectiveImport{}            -> InfectiveImport_
  CoInfectiveImport{}          -> CoInfectiveImport_


data TCWarning
  = TCWarning
    { tcWarningRange :: Range
        -- ^ Range where the warning was raised
    , tcWarning   :: Warning
        -- ^ The warning itself
    , tcWarningPrintedWarning :: Doc
        -- ^ The warning printed in the state and environment where it was raised
    , tcWarningCached :: Bool
        -- ^ Should the warning be affected by caching.
    }
  deriving Show


tcWarningOrigin :: TCWarning -> SrcFile
tcWarningOrigin = rangeFile . tcWarningRange

instance HasRange TCWarning where
  getRange = tcWarningRange

-- used for merging lists of warnings
instance Eq TCWarning where
  x == y = equalHeadConstructors (tcWarning x) (tcWarning y)
            && getRange x == getRange y

equalHeadConstructors :: Warning -> Warning -> Bool
equalHeadConstructors = (==) `on` toConstr

getPartialDefs :: ReadTCState tcm => tcm [QName]
getPartialDefs = do
  tcst <- getTCState
  return $ mapMaybe (extractQName . tcWarning)
         $ tcst ^. stTCWarnings where

    extractQName :: Warning -> Maybe QName
    extractQName (CoverageIssue f _) = Just f
    extractQName _                   = Nothing

---------------------------------------------------------------------------
-- * Type checking errors
---------------------------------------------------------------------------

-- | Information about a call.

data CallInfo = CallInfo
  { callInfoTarget :: QName
    -- ^ Target function name.
  , callInfoRange :: Range
    -- ^ Range of the target function.
  , callInfoCall :: Closure Term
    -- ^ To be formatted representation of the call.
  } deriving (Data, Show)

-- no Eq, Ord instances: too expensive! (see issues 851, 852)

-- | We only 'show' the name of the callee.
instance Pretty CallInfo where pretty = pretty . callInfoTarget
instance AllNames CallInfo where allNames = singleton . callInfoTarget

-- UNUSED, but keep!
-- -- | Call pathes are sequences of 'CallInfo's starting from a 'callSource'.
-- data CallPath = CallPath
--   { callSource :: QName
--     -- ^ The originator of the first call.
--   , callInfos :: [CallInfo]
--     -- ^ The calls, in order from source to final target.
--   }
--   deriving (Show)

-- -- | 'CallPath'es can be connected, but there is no empty callpath.
-- --   Thus, they form a semigroup, but we choose to abuse 'Monoid'.
-- instance Monoid CallPath where
--   mempty = __IMPOSSIBLE__
--   mappend (CallPath src cs) (CallPath _ cs') = CallPath src $ cs ++ cs'

-- | Information about a mutual block which did not pass the
-- termination checker.

data TerminationError = TerminationError
  { termErrFunctions :: [QName]
    -- ^ The functions which failed to check. (May not include
    -- automatically generated functions.)
  , termErrCalls :: [CallInfo]
    -- ^ The problematic call sites.
  } deriving (Data, Show)

-- | Error when splitting a pattern variable into possible constructor patterns.
data SplitError
  = NotADatatype        (Closure Type)  -- ^ Neither data type nor record.
  | IrrelevantDatatype  (Closure Type)  -- ^ Data type, but in irrelevant position.
  | ErasedDatatype      (Closure Type)  -- ^ Data type, but in erased position.
  | CoinductiveDatatype (Closure Type)  -- ^ Split on codata not allowed.
  -- UNUSED, but keep!
  -- -- | NoRecordConstructor Type  -- ^ record type, but no constructor
  | UnificationStuck
    { cantSplitConName  :: QName        -- ^ Constructor.
    , cantSplitTel      :: Telescope    -- ^ Context for indices.
    , cantSplitConIdx   :: Args         -- ^ Inferred indices (from type of constructor).
    , cantSplitGivenIdx :: Args         -- ^ Expected indices (from checking pattern).
    , cantSplitFailures :: [UnificationFailure] -- ^ Reason(s) why unification got stuck.
    }
  | CosplitCatchall
      -- ^ Copattern split with a catchall
  | CosplitNoTarget
      -- ^ We do not know the target type of the clause.
  | CosplitNoRecordType (Closure Type)
      -- ^ Target type is not a record type.
  | CannotCreateMissingClause QName (Telescope,[NamedArg DeBruijnPattern]) Doc (Closure (Abs Type))

  | GenericSplitError String
  deriving (Show)

data NegativeUnification
  = UnifyConflict Telescope Term Term
  | UnifyCycle Telescope Int Term
  deriving (Show)

data UnificationFailure
  = UnifyIndicesNotVars Telescope Type Term Term