TH.Utilities

Miscellaneous Template Haskell utilities, added as needed by packages in the th-utilities repo and elsewhere.

Documentation

tyVarBndrName :: TyVarBndr -> Name

Get the Name of a TyVarBndr

unAppsT :: Type -> [Type]

Breaks a type application like A b c into [A, b, c]. In other words, it descends leftwards down AppT constructors, and yields a list of the results.

typeToNamedCon :: Type -> Maybe (Name, [Type])

Given a Type, returns a Just value if it's a named type constructor applied to arguments. This value contains the name of the type and a list of arguments.

expectTyCon1 :: Name -> Type -> Q Type

Expect the provided type to be an application of a regular type to one argument, otherwise fail with a message. This will also work if the name is a promoted data constructor (PromotedT).

expectTyCon2 :: Name -> Type -> Q (Type, Type)

Expect the provided type to be an application of a regular type to two arguments, otherwise fail with a message. This will also work if the name is a promoted data constructor (PromotedT).

proxyE :: TypeQ -> ExpQ

Given a type, construct the expression (Proxy :: Proxy ty).

dequalify :: Name -> Name

Construct a plain name (mkName) based on the given name. This is useful for cases where TH doesn't expect a unique name.

freeVarsT :: Type -> [Name]

Get the free type variables of a Type.

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

Utility to conveniently handle change to InstanceD API in template-haskell-2.11.0

fromPlainInstanceD :: Dec -> Maybe (Cxt, Type, [Dec])

Utility to conveniently handle change to InstanceD API in template-haskell-2.11.0

data ExpLifter

Hack to enable putting expressions inside lift-ed TH data. For example, you could do

    main = print $(lift [ExpLifter [e| 1 + 1 |],  ExpLifter [e| 2 |]])

Here, lift is working on a value of type [ExpLifter]. The code generated by lift constructs a list with the ExpLifter expressions providing the element values.

Without ExpLifter, lift tends to just generate code involving data construction. With ExpLifter, you can put more complicated expression into this construction.

Constructors

ExpLifter ExpQ

Instances

Lift ExpLifter