GHC.SourceGen.Decl

This module provides combinators for constructing Haskell declarations.

Documentation

type HsDecl' = HsDecl GhcPs

A Haskell declaration, as it is represented after the parsing step.

Instances:

• HasValBind
• HasPatBind

Type declarations

type' :: OccNameStr -> [HsTyVarBndr'] -> HsType' -> HsDecl'

Declares a type synonym.

type A a b = B b a
=====
type' "A" [bvar "a", bvar "b"] $ var "B" @@ var "b" @@ var "a"

newtype' :: OccNameStr -> [HsTyVarBndr'] -> ConDecl' -> [HsDerivingClause'] -> HsDecl'

A newtype declaration.

newtype Const a b = Const a deriving Eq
=====
newtype' "Const" [bvar "a", bvar "b"]
   (conDecl "Const" [var "a"])
   [var "Show"]

data' :: OccNameStr -> [HsTyVarBndr'] -> [ConDecl'] -> [HsDerivingClause'] -> HsDecl'

A data declaration.

data Either a b = Left a | Right b
   deriving Show
=====
data' "Either" [bvar "a", bvar "b"]
  [ conDecl "Left" [var "a"]
  , conDecl "Right" [var "b"]
  ]
  [var "Show"]

Data constructors

type ConDecl' = ConDecl GhcPs

prefixCon :: OccNameStr -> [Field] -> ConDecl'

Declares a Haskell-98-style prefix constructor for a data or type declaration.

Foo a Int
=====
prefixCon "Foo" [field (var "a"), field (var "Int")]

infixCon :: Field -> OccNameStr -> Field -> ConDecl'

Declares a Haskell-98-style infix constructor for a data or type declaration.

A b :+: C d
=====
infixCon (field (var "A" @@ var "b")) ":+:" (field (Var "C" @@ var "d"))

recordCon :: OccNameStr -> [(OccNameStr, Field)] -> ConDecl'

Declares Haskell-98-style record constructor for a data or type declaration.

A { x :: B, y :: C }
=====
recordCon "A" [("x", var "B"), ("y", var "C")]

data Field

An individual argument of a data constructor. Contains a type for the field, and whether the field is strict or lazy.

field :: HsType' -> Field

A field with no explicit strictness annotations.

A b
=====
field $ var "A" @@ var "b"

strict :: Field -> Field

Give a field an explicit strictness annotation. Overrides any such previous annotations (for example, from lazy).

!(A b)
=====
strict $ field $ var "A" @@ var "b"

lazy :: Field -> Field

Give a field an explicit laziness annotation. This feature is useful in combination with the StrictData extension. Overrides any such previous annotations (for example, from strict).

!(A b)
=====
strict $ field $ var "A" @@ var "b"

Deriving clauses

type HsDerivingClause' = HsDerivingClause GhcPs

deriving' :: [HsType'] -> HsDerivingClause'

derivingStock :: [HsType'] -> HsDerivingClause'

derivingAnyclass :: [HsType'] -> HsDerivingClause'

derivingNewtype :: [HsType'] -> HsDerivingClause'

derivingVia :: HsType' -> [HsType'] -> HsDerivingClause'

A DerivingVia clause.

deriving (Eq, Show) via T
=====
derivingVia (var "T") [var "Eq", var "Show"]

Available with ghc>=8.6.

standaloneDeriving :: HsType' -> HsDecl'

standaloneDerivingStock :: HsType' -> HsDecl'

standaloneDerivingNewtype :: HsType' -> HsDecl'

standaloneDerivingAnyclass :: HsType' -> HsDecl'

Class declarations

class'

Arguments

:: [HsType']

Context

-> OccNameStr

Class name

-> [HsTyVarBndr']

Type parameters

-> [ClassDecl]

Class declarations

-> HsDecl'

A class declaration.

class (Real a, Enum a) => Integral a where
  divMod :: a -> a -> (a, a)
  div :: a -> a -> a
  div x y = fst (divMod x y)
=====
let a = var "a"
in class'
     [var "Real" @@ a, var "Enum" @@ a]
     "Integral"
     [bvar "a"]
     [ typeSig "divMod" $ a --> a --> tuple [a, a]
     , typeSig "div" $ a --> a --> a
     , funBind "div"
         $ match [bvar "x", bvar "y"]
            $ var "fst" @@ (var "divMod" @@ var "x" @@ var "y")
     ]

data ClassDecl

A definition that can appear in the body of a class declaration.

ClassDecl definitions may be constructed using funDep or using the instance of HasValBind. For more details, see the documentation of that function, and of GHC.SourceGen.Binds overall.

Instances

HasValBind ClassDecl

Defined in GHC.SourceGen.Decl

Methods

sigB :: Sig' -> ClassDecl

bindB :: HsBind' -> ClassDecl

funDep :: [RdrNameStr] -> [RdrNameStr] -> ClassDecl

A functional dependency for a class.

| a, b -> c
=====
funDep ["a", "b"] ["c"]

class Ident a b | a -> b, b -> a where
  ident :: a -> b
=====
class' [] "Ident" ["a", "b"]
   [ funDep ["a"] ["b"]
   , funDep ["b"] ["a"]
   , typeSig "ident" $ var "a" --> var "b"
   ]

Instance declarations

instance' :: HsType' -> [RawInstDecl] -> HsDecl'

An instance declaration.

instance Show Bool where
  show :: Bool -> String -- Requires the InstanceSigs extension
  show True = "True"
  show False = "False"
=====
instance' (var "Show" @@ var "Bool")
  [ typeSig "show" $ var "Bool" --> var "String"
  , funBinds "show"
      [ match [bvar "True"] $ string "True"
      , match [bvar "False"] $ string "False"
      ]
  ]

data RawInstDecl

A definition that can appear in the body of an instance declaration.

RawInstDecl definitions may be constructed using its class instances, e.g., HasValBind. For more details, see the documentation of those classes.

Instances

HasValBind RawInstDecl

Defined in GHC.SourceGen.Decl

Methods

sigB :: Sig' -> RawInstDecl

bindB :: HsBind' -> RawInstDecl

HasTyFamInst RawInstDecl

Defined in GHC.SourceGen.Decl

Methods

tyFamInstD :: TyFamInstDecl' -> RawInstDecl

class HasTyFamInst t where

Terms which can contain a type instance declaration.

To use this class, call tyFamInst.

Methods

tyFamInstD :: TyFamInstDecl' -> t

Instances

HasTyFamInst RawInstDecl

Defined in GHC.SourceGen.Decl

Methods

tyFamInstD :: TyFamInstDecl' -> RawInstDecl

HasTyFamInst HsDecl'

Defined in GHC.SourceGen.Decl

Methods

tyFamInstD :: TyFamInstDecl' -> HsDecl'

tyFamInst :: HasTyFamInst t => RdrNameStr -> [HsType'] -> HsType' -> t

A type family instance.

type Elt String = Char
=====
tyFamInst "Elt" [var "String"] (var "Char")

Pattern synonyms

patSynSigs :: [OccNameStr] -> HsType' -> HsDecl'

Declares multiple pattern signatures of the same type.

pattern F, G :: T
=====
patSynSigs ["F", "G"] $ var "T"

patSynSig :: OccNameStr -> HsType' -> HsDecl'

Declares a pattern signature and its type.

pattern F :: T
=====
patSynSigs "F" $ var "T"

patSynBind :: OccNameStr -> [OccNameStr] -> Pat' -> HsDecl'

Defines a pattern signature.

pattern F a b = G b a
=====
patSynBind "F" ["a", "b"] $ conP "G" [bvar "b", bvar "a"]