[GHC] #15437: Internal error when applying a scoped type variable inside a typed expression quotation

25 Jul 2018


      #15437: Internal error when applying a scoped type variable inside a typed
expression quotation
-------------------------------------+-------------------------------------
           Reporter:  dminuoso       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}

 import TestMod

 f :: Int
 f = $$(foo)

 main :: IO ()
 main = main
 }}}

 {{{#!hs
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TypeApplications #-}

 module TestMod where

 import Language.Haskell.TH.Syntax (Q, TExp)

 get :: forall a. Int
 get = 1

 foo :: forall a. Q (TExp Int)
 foo = [|| get @a ||]
 }}}

 {{{
 Test.hs:6:8: error:
     • The exact Name ‘a’ is not in scope
         Probable cause: you used a unique Template Haskell name (NameU),
         perhaps via newName, but did not bind it
         If that's it, then -ddump-splices might be useful
     • In the result of the splice:
         $foo
       To see what the splice expanded to, use -ddump-splices
       In the Template Haskell splice $$(foo)
       In the expression: $$(foo)
   |
 6 | f = $$(foo)
   |        ^^^

 Test.hs:6:8: error:
     • GHC internal error: ‘a’ is not in scope during type checking, but it
 passed the renamer
       tcl_env of environment: [r3Kl :-> Identifier[f::Int, TopLevelLet []
 True],
                                r3PI :-> Identifier[main::IO (),
 TopLevelLet [r3PI :-> main] True]]
     • In the type ‘a’
       In the expression: get @a
       In the result of the splice:
         $foo
       To see what the splice expanded to, use -ddump-splices
   |
 6 | f = $$(foo)
   |
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15437
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