Safe Haskell	Safe
Language	Haskell2010

Type.Funspection.Core

Description

Synopsis

type family EnableIf (condition :: Bool) (a :: Type) :: Type where ...
newtype Return (a :: Type) where
- Return :: {..} -> Return a
type family ReturnOf (f :: Type) :: Type where ...
type family CanReturn (r :: Type) (f :: Type) :: Bool where ...
type family TaggedReturn (r :: Type) (f :: Type) :: Type where ...
type TagReturn (r :: Type) (f :: Type) = TagReturn' (TaggedReturn r f) f
tagReturn :: forall r f. TagReturn r f => Proxy r -> f -> TaggedReturn r f
type family UntaggedReturn (f :: Type) :: Type where ...
type UntagReturn (f :: Type) = UntagReturn' f
untagReturn :: UntagReturn f => f -> UntaggedReturn f

Documentation

type family EnableIf (condition :: Bool) (a :: Type) :: Type where ... Source #

This only compiles when the supplied type-level condition is True

Equations

EnableIf True a = a

newtype Return (a :: Type) where Source #

This can be used to make the return type of a function unambigious in pattern matching contexts. (Ambiguity can occur because functions in Haskell are implicitly curried.)

Constructors

Return
Fields :: { unReturn :: a } -> Return a

type family ReturnOf (f :: Type) :: Type where ... Source #

Yeilds the ultimate return type of a function (after it has been fully applied).

Since this never resolves to a function type as the return type, one must wrap desired function returns. Return can be used for such wrapping.

Equations

ReturnOf (a -> b) = ReturnOf b
ReturnOf r = r

type family CanReturn (r :: Type) (f :: Type) :: Bool where ... Source #

Determines whether a function of type f can return the type r.

Equations

CanReturn r r = True
CanReturn r (a -> b) = CanReturn r b
CanReturn r r' = False

type family TaggedReturn (r :: Type) (f :: Type) :: Type where ... Source #

Tags the desired return type r of f with Return.

Note: This fails to compile if r is not a valid return type of f.

Examples:

TaggedReturn Int Int ~ (Return Int)
TaggedReturn Int (Char -> Char -> Int) ~ Char -> Char -> Return Int
TaggedReturn (Char -> Int) (Char -> Char -> Int) ~ Char -> Return (Char -> Int)

Equations

TaggedReturn r r = Return r
TaggedReturn r (a -> b) = a -> TaggedReturn r b

type TagReturn (r :: Type) (f :: Type) = TagReturn' (TaggedReturn r f) f Source #

The constraint required for tagReturn.

tagReturn :: forall r f. TagReturn r f => Proxy r -> f -> TaggedReturn r f Source #

Transforms a function of type f into a new function of type TaggedReturn r f

type family UntaggedReturn (f :: Type) :: Type where ... Source #

Removes the Return tag from function signature of f.

This is the inverse of TaggedReturn in the sense that the following holds:

UntaggedReturn (TaggedReturn r f) ~ f

Note: This fails to compile if Return r is not a valid return type of f.

Equations

UntaggedReturn (Return r) = r
UntaggedReturn (a -> b) = a -> UntaggedReturn b

type UntagReturn (f :: Type) = UntagReturn' f Source #

The constraint required for untagReturn.

untagReturn :: UntagReturn f => f -> UntaggedReturn f Source #

Transforms a function of type TaggedReturn r f into a new function of type f