Skip to content

Instantly share code, notes, and snippets.

@LSLeary

LSLeary/Is.hs

Last active January 24, 2026 09:45
Show Gist options

  • Select an option

    Learn more about clone URLs
  • Save LSLeary/7165377d1a28bf76aa4c0aae189a6968 to your computer and use it in GitHub Desktop.

Select an option

Learn more about clone URLs
Save LSLeary/7165377d1a28bf76aa4c0aae189a6968 to your computer and use it in GitHub Desktop.
Download ZIP
Match on type
Raw
Is.hs
{-#
LANGUAGE
GHC2021, PatternSynonyms, ViewPatterns, ExplicitNamespaces, GADTs
#-}
module Is (pattern Is) where
-- base
import Type.Reflection
import Data.Type.Equality (type (~~))
pattern Is
:: forall {k} {l} (a :: k) (b :: l)
. Typeable a
=> a ~~ b
=> TypeRep b
pattern Is <- (eqTypeRep (typeRep @a) -> Just HRefl)
where Is = typeRep
_test :: forall {proxy} a. Typeable a => proxy a -> String
_test _ = case typeRep @a of
Is @Bool -> "bool"
Is @Double -> "double"
_ -> "dunno"
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment