Data.Comp.Derive.Utils

This module defines some utility functions for deriving instances for functor based type classes.

Documentation

data DataInfo

Constructors

forall flag. DataInfo Cxt Name [TyVarBndr flag] [Con] [DerivClause]

abstractNewtypeQ :: Q Info -> Q (Maybe DataInfo)

This is the Q-lifted version of 'abstractNewtype.

abstractNewtype :: Info -> Maybe DataInfo

This function abstracts away newtype declaration, it turns them into data declarations.

normalCon :: Con -> (Name, [StrictType], Maybe Type)

This function provides the name and the arity of the given data constructor, and if it is a GADT also its type.

normalCon' :: Con -> (Name, [Type], Maybe Type)

normalConExp :: Con -> Q (Name, [Type], Maybe Type)

Same as normalCon' but expands type synonyms.

normalConStrExp :: Con -> Q (Name, [StrictType], Maybe Type)

Same as normalConExp' but retains strictness annotations.

getBinaryFArg :: Type -> Maybe Type -> Type

Auxiliary function to extract the first argument of a binary type application (the second argument of this function). If the second argument is Nothing or not of the right shape, the first argument is returned as a default.

getUnaryFArg :: Type -> Maybe Type -> Type

Auxiliary function to extract the first argument of a type application (the second argument of this function). If the second argument is Nothing or not of the right shape, the first argument is returned as a default.

abstractConType :: Con -> (Name, Int)

This function provides the name and the arity of the given data constructor.

tyVarBndrName :: TyVarBndr flag -> Name

This function returns the name of a bound type variable

containsType :: Type -> Type -> Bool

containsType' :: Type -> Type -> [Int]

newNames :: Int -> String -> Q [Name]

This function provides a list (of the given length) of new names based on the given string.

tupleTypes :: Int -> Int -> [Name]

derive :: [Name -> Q [Dec]] -> [Name] -> Q [Dec]

Helper function for generating a list of instances for a list of named signatures. For example, in order to derive instances Functor and ShowF for a signature Exp, use derive as follows (requires Template Haskell):

$(derive [makeFunctor, makeShowF] [''Exp])

mkClassP :: Name -> [Type] -> Type

Apply a class name to type arguments to construct a type class constraint.

isEqualP :: Type -> Maybe (Type, Type)

This function checks whether the given type constraint is an equality constraint. If so, the types of the equality constraint are returned.

mkInstanceD :: Cxt -> Type -> [Dec] -> Dec

liftSumGen :: Name -> Name -> Name -> Q [Dec]

This function lifts type class instances over sums ofsignatures. To this end it assumes that it contains only methods with types of the form f t1 .. tn -> t where f is the signature that is used to construct sums. Since this function is generic it assumes as its first argument the name of the function that is used to lift methods over sums i.e. a function of type

(f t1 .. tn -> t) -> (g t1 .. tn -> t) -> ((f :+: g) t1 .. tn -> t)

where :+: is the sum type constructor. The second argument to this function is expected to be the name of that constructor. The last argument is the name of the class whose instances should be lifted over sums.

findSig :: [Name] -> [Dec] -> Q (Maybe ([Name], [Name]))