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Template Haskell mistakenly assumes "FUN" is built-in syntax

    • Closed Issue created by Vladislav Zavialov @int-index

    Basically the same issue as #24702 (closed) but with "FUN".

    The following works as expected:

    {-# LANGUAGE TemplateHaskell #-}
module T where

import Language.Haskell.TH

data Fun a b = MkFun (a -> b)

evenFun :: $(conT (mkName "Fun")) Int Bool
evenFun = MkFun even
    [1 of 1] Compiling T                ( Test.hs, interpreted )
Ok, one module loaded.

    But if Fun is capitalized, it results in a bogus error:

    {-# LANGUAGE TemplateHaskell #-}
module T where

import Language.Haskell.TH

data FUN a b = MkFUN (a -> b)

evenFUN :: $(conT (mkName "FUN")) Int Bool
evenFUN = MkFUN even
    [1 of 1] Compiling T                ( Test.hs, interpreted )
Test.hs:8:12: error: [GHC-83865]
    • Expecting one more argument to ‘GHC.Prim.FUN Int Bool’
      Expected a type, but ‘GHC.Prim.FUN Int Bool’ has kind ‘* -> *’
    • In the type signature: evenFUN :: GHC.Prim.FUN Int Bool
  |
8 | evenFUN :: $(conT (mkName "FUN")) Int Bool
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Test.hs:8:35: error: [GHC-83865]
    • Expected kind ‘GHC.Types.Multiplicity’, but ‘Int’ has kind ‘*’
    • In the first argument of ‘GHC.Prim.FUN’, namely ‘Int’
      In the type signature: evenFUN :: GHC.Prim.FUN Int Bool
  |
8 | evenFUN :: $(conT (mkName "FUN")) Int Bool
  |                                   ^^^

Failed, unloaded all modules.

    I'll submit a fix.

    Edited
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