Data.OverloadedLabels

This module defines the IsLabel class which is used by the OverloadedLabels language extension. See the wiki page for more details.

The key idea is that when GHC sees an occurrence of the new overloaded label syntax #foo, it is replaced with

fromLabel (proxy# :: Proxy# "foo") :: alpha

plus a wanted constraint IsLabel "foo" alpha.

On GHC >=8.0.1 we just reexport GHC.OverloadedLabels module.

Oveloaded Labels

module GHC.OverloadedLabels

data Label l

Since 0.4.2.0

Constructors

Label (Proxy# l)

Instances

(~) Symbol l1 l2 => IsLabel l1 (Label l2)

Since 0.4.2.0

Methods

fromLabel :: Proxy# Symbol l1 -> Label l2

KnownSymbol l => Show (Label l)

Since 0.4.2.0

Methods

showsPrec :: Int -> Label l -> ShowS

show :: Label l -> String

showList :: [Label l] -> ShowS

getLabel :: Label l -> Label l

Type restricted identity function.

Since 0.4.2.0

showLabel :: KnownSymbol l => Label l -> String

Type restricted version of show.

>>> showLabel #foo
#foo

Since 0.4.2.0

unLabel :: IsLabel l a => Label l -> a

Same as fromLabel, but works for Label data type.

Since 0.4.2.0