Data.Parameterized.TH.GADT

This module declares template Haskell primitives so that it is easier to work with GADTs that have many constructors.

Documentation

structuralEquality :: TypeQ -> [(TypePat, ExpQ)] -> ExpQ

declareStructuralEquality declares a structural equality predicate.

structuralTypeEquality :: TypeQ -> [(TypePat, ExpQ)] -> ExpQ

structuralTypeEquality f returns a function with the type: forall x y . f x -> f y -> Maybe (x :~: y)

structuralTypeOrd

Arguments

:: TypeQ

-> [(TypePat, ExpQ)]

List of type patterns to match.

-> ExpQ

structuralTypeEquality f returns a function with the type: forall x y . f x -> f y -> OrderingF x y

This implementation avoids matching on both the first and second parameters in a simple case expression in order to avoid stressing GHC's coverage checker. In the case that the first and second parameters have unique constructors, a simple numeric comparison is done to compute the result.

structuralTraversal :: TypeQ -> [(TypePat, ExpQ)] -> ExpQ

structuralTraversal tp generates a function that applies a traversal f to the subterms with free variables in tp.

structuralShowsPrec :: TypeQ -> ExpQ

structuralShow tp generates a function with the type tp -> ShowS that shows the constructor.

structuralHash :: TypeQ -> ExpQ

structuralHash tp generates a function with the type Int -> tp -> Int that hashes type.

class PolyEq u v where

A polymorphic equality operator that generalizes TestEquality.

Minimal complete definition

polyEqF

Methods

polyEqF :: u -> v -> Maybe (u :~: v)

polyEq :: u -> v -> Bool

Instances

PolyEq (NatRepr m) (NatRepr n)

Methods

polyEqF :: NatRepr m -> NatRepr n -> Maybe ((* :~: NatRepr m) (NatRepr n))

polyEq :: NatRepr m -> NatRepr n -> Bool

TestEquality k f => PolyEq (Assignment k f x) (Assignment k f y)

Methods

polyEqF :: Assignment k f x -> Assignment k f y -> Maybe ((* :~: Assignment k f x) (Assignment k f y))

polyEq :: Assignment k f x -> Assignment k f y -> Bool

Template haskell utilities that may be useful in other contexts.

type DataD = DatatypeInfo

lookupDataType' :: Name -> Q DatatypeInfo

asTypeCon :: Monad m => String -> Type -> m Name

conPat

Arguments

:: ConstructorInfo

constructor information

-> String

generated name prefix

-> Q (Pat, [Name])

pattern and bound names

Given a constructor and string, this generates a pattern for matching the expression, and the names of variables bound by pattern in order they appear in constructor.

data TypePat

Constructors

TypeApp TypePat TypePat

The application of a type.

AnyType

Match any type.

DataArg Int

Match the ith argument of the data type we are traversing.

ConType TypeQ

Match a ground type.

dataParamTypes :: DatatypeInfo -> [Type]

assocTypePats :: [Type] -> [(TypePat, v)] -> Type -> Q (Maybe v)

Find value associated with first pattern that matches given pat if any.