express-1.0.14: Dynamically-typed expressions involving function application and variables.
Copyright(c) 2019-2024 Rudy Matela
License3-Clause BSD (see the file LICENSE)
MaintainerRudy Matela <rudy@matela.com.br>
Safe HaskellSafe-Inferred
LanguageHaskell2010

Data.Express.Utils.TH

Description

Template Haskell utilities.

Synopsis

Documentation

normalizeType :: Name -> Q (Type, [Type]) Source #

Normalizes a type by applying it to necessary type variables making it accept zero type parameters. The normalized type is paired with a list of necessary type variables.

> putStrLn $(stringE . show =<< normalizeType ''Int)
(ConT ''Int, [])
> putStrLn $(stringE . show =<< normalizeType ''Maybe)
(AppT (ConT ''Maybe) (VarT ''a),[VarT ''a])
> putStrLn $(stringE . show =<< normalizeType ''Either)
(AppT (AppT (ConT ''Either) (VarT ''a)) (VarT ''b),[VarT ''a,VarT ''b])
> putStrLn $(stringE . show =<< normalizeType ''[])
(AppT (ConT ''[]) (VarT a),[VarT a])

normalizeTypeUnits :: Name -> Q Type Source #

Normalizes a type by applying it to units to make it star-kinded. (cf. normalizeType)

normalizeTypeUnits ''Int    === [t| Int |]
normalizeTypeUnits ''Maybe  === [t| Maybe () |]
normalizeTypeUnits ''Either === [t| Either () () |]

isInstanceOf :: Name -> Name -> Q Bool Source #

Given a type name and a class name, returns whether the type is an instance of that class. The given type must be star-kinded ( * ) and the given class double-star-kinded ( * -> * .

> putStrLn $(stringE . show =<< ''Int `isInstanceOf` ''Num)
True
> putStrLn $(stringE . show =<< ''Int `isInstanceOf` ''Fractional)
False

isntInstanceOf :: Name -> Name -> Q Bool Source #

The negation of isInstanceOf.

typeArity :: Name -> Q Int Source #

Given a type name, return the number of arguments taken by that type. Examples in partially broken TH:

> putStrLn $(stringE . show =<< typeArity ''Int)
0
> putStrLn $(stringE . show =<< typeArity ''Maybe)
1
> putStrLn $(stringE . show =<< typeArity ''Either)
2
> putStrLn $(stringE . show =<< typeArity ''[])
1
> putStrLn $(stringE . show =<< typeArity ''(,))
2
> putStrLn $(stringE . show =<< typeArity ''(,,))
3
> putStrLn $(stringE . show =<< typeArity ''String)
0

This works for data and newtype declarations and it is useful when generating typeclass instances.

typeConstructors :: Name -> Q [(Name, [Type])] Source #

Given a type Name, returns a list of its type constructor Names paired with the type arguments they take. the type arguments they take.

> putStrLn $(stringE . show =<< typeConstructors ''Bool)
[ ('False, [])
, ('True, [])
]
> putStrLn $(stringE . show =<< typeConstructors ''[])
[ ('[], [])
, ('(:), [VarT ''a, AppT ListT (VarT ''a)])
]
> putStrLn $(stringE . show =<< typeConstructors ''(,))
[('(,), [VarT (mkName "a"), VarT (mkName "b")])]
> data Point  =  Pt Int Int
> putStrLn $(stringE . show =<< typeConstructors ''Point)
[('Pt,[ConT ''Int, ConT ''Int])]

isTypeSynonym :: Name -> Q Bool Source #

Is the given Name a type synonym?

> putStrLn $(stringE . show =<< isTypeSynonym 'show)
False
> putStrLn $(stringE . show =<< isTypeSynonym ''Char)
False
> putStrLn $(stringE . show =<< isTypeSynonym ''String)
True

typeSynonymType :: Name -> Q Type Source #

Resolves a type synonym.

> putStrLn $(stringE . show =<< typeSynonymType ''String)
AppT ListT (ConT ''Char)

lookupValN :: String -> Q Name Source #

Lookups the name of a value throwing an error when it is not found.

> putStrLn $(stringE . show =<< lookupValN "show")
'show

showJustName :: Name -> String Source #

Encodes a Name as a String. This is useful when generating error messages.

> showJustName ''Int
"Int"
> showJustName ''String
"String"
> showJustName ''Maybe
"Maybe"

unboundVars :: Type -> [Name] Source #

Lists all unbound variables in a type. This intentionally excludes the ForallT constructor.

toBounded :: Type -> Type Source #

Binds all unbound variables using a ForallT constructor. (cf. unboundVars)

toBoundedQ :: TypeQ -> TypeQ Source #

Same as toBounded but lifted over Q