module Language.PureScript.Sugar.CaseDeclarations (
desugarCases,
desugarCasesModule
) where
import Data.Monoid ((<>))
import Data.List (nub, groupBy)
import Control.Applicative
import Control.Monad ((<=<), forM, join, unless, replicateM)
import Control.Monad.Error.Class
import Language.PureScript.Names
import Language.PureScript.AST
import Language.PureScript.Environment
import Language.PureScript.Errors
import Language.PureScript.Supply
import Language.PureScript.Traversals
import Language.PureScript.TypeChecker.Monad (guardWith)
isLeft :: Either a b -> Bool
isLeft (Left _) = True
isLeft (Right _) = False
desugarCasesModule :: [Module] -> SupplyT (Either ErrorStack) [Module]
desugarCasesModule ms = forM ms $ \(Module name ds exps) ->
rethrow (strMsg ("Error in module " ++ show name) <>) $
Module name <$> (desugarCases <=< desugarAbs $ ds) <*> pure exps
desugarAbs :: [Declaration] -> SupplyT (Either ErrorStack) [Declaration]
desugarAbs = flip parU f
where
(f, _, _) = everywhereOnValuesM return replace return
replace :: Expr -> SupplyT (Either ErrorStack) Expr
replace (Abs (Right binder) val) = do
ident <- Ident <$> freshName
return $ Abs (Left ident) $ Case [Var (Qualified Nothing ident)] [CaseAlternative [binder] (Right val)]
replace other = return other
desugarCases :: [Declaration] -> SupplyT (Either ErrorStack) [Declaration]
desugarCases = desugarRest <=< fmap join . flip parU toDecls . groupBy inSameGroup
where
desugarRest :: [Declaration] -> SupplyT (Either ErrorStack) [Declaration]
desugarRest (TypeInstanceDeclaration name constraints className tys ds : rest) =
(:) <$> (TypeInstanceDeclaration name constraints className tys <$> desugarCases ds) <*> desugarRest rest
desugarRest (ValueDeclaration name nameKind bs result : rest) =
let (_, f, _) = everywhereOnValuesTopDownM return go return
f' (Left gs) = Left <$> mapM (pairM return f) gs
f' (Right v) = Right <$> f v
in (:) <$> (ValueDeclaration name nameKind bs <$> f' result) <*> desugarRest rest
where
go (Let ds val') = Let <$> desugarCases ds <*> pure val'
go other = return other
desugarRest (PositionedDeclaration pos d : ds) = do
(d' : ds') <- desugarRest (d : ds)
return (PositionedDeclaration pos d' : ds')
desugarRest (d : ds) = (:) d <$> desugarRest ds
desugarRest [] = pure []
inSameGroup :: Declaration -> Declaration -> Bool
inSameGroup (ValueDeclaration ident1 _ _ _) (ValueDeclaration ident2 _ _ _) = ident1 == ident2
inSameGroup (PositionedDeclaration _ d1) d2 = inSameGroup d1 d2
inSameGroup d1 (PositionedDeclaration _ d2) = inSameGroup d1 d2
inSameGroup _ _ = False
toDecls :: [Declaration] -> SupplyT (Either ErrorStack) [Declaration]
toDecls [ValueDeclaration ident nameKind bs (Right val)] | all isVarBinder bs = do
let args = map (\(VarBinder arg) -> arg) bs
body = foldr (Abs . Left) val args
guardWith (strMsg "Overlapping function argument names") $ length (nub args) == length args
return [ValueDeclaration ident nameKind [] (Right body)]
toDecls ds@(ValueDeclaration ident _ bs result : _) = do
let tuples = map toTuple ds
unless (all ((== length bs) . length . fst) tuples) $
throwError $ mkErrorStack ("Argument list lengths differ in declaration " ++ show ident) Nothing
unless (not (null bs) || isLeft result) $
throwError $ mkErrorStack ("Duplicate value declaration '" ++ show ident ++ "'") Nothing
caseDecl <- makeCaseDeclaration ident tuples
return [caseDecl]
toDecls (PositionedDeclaration pos d : ds) = do
(d' : ds') <- rethrowWithPosition pos $ toDecls (d : ds)
return (PositionedDeclaration pos d' : ds')
toDecls ds = return ds
isVarBinder :: Binder -> Bool
isVarBinder (VarBinder _) = True
isVarBinder _ = False
toTuple :: Declaration -> ([Binder], Either [(Guard, Expr)] Expr)
toTuple (ValueDeclaration _ _ bs result) = (bs, result)
toTuple (PositionedDeclaration _ d) = toTuple d
toTuple _ = error "Not a value declaration"
makeCaseDeclaration :: Ident -> [([Binder], Either [(Guard, Expr)] Expr)] -> SupplyT (Either ErrorStack) Declaration
makeCaseDeclaration ident alternatives = do
let argPattern = length . fst . head $ alternatives
args <- map Ident <$> replicateM argPattern freshName
let
vars = map (Var . Qualified Nothing) args
binders = [ CaseAlternative bs result | (bs, result) <- alternatives ]
value = foldr (Abs . Left) (Case vars binders) args
return $ ValueDeclaration ident Value [] (Right value)