Re: [GHC] #13642: GHCi 8.2 simply ignores TH splice using datatype with a forall'd kind signature

3 May 2017

      #13642: GHCi 8.2 simply ignores TH splice using datatype with a forall'd kind
signature
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.2.1-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Actually, it extends even beyond GHCi! If you put this into a module:

 {{{#!hs
 {-# LANGUAGE GADTs, TypeInType, TemplateHaskell, RankNTypes #-}
 module Bug where

 import Data.Kind (Type)
 import Language.Haskell.TH (stringE, pprint)

 main :: IO ()
 main = putStrLn $([d| data Foo :: forall a. a -> Type where MkFoo :: Foo
 Int |] >>= string
 E . pprint)
 }}}

 Then some interesting things happen if you try to compile this. If you try
 to load it into GHCi, you get this:

 {{{
 $ /opt/ghc/8.2.1/bin/ghci Bug.hs
 GHCi, version 8.2.0.20170427: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )
 Failed, modules loaded: none.
 }}}

 Apparently the module fails to compile, despite the fact that no errors
 were emitted during compilation. Something similar happens if you directly
 invoke `ghc` on it:

 {{{
 $ /opt/ghc/8.2.1/bin/ghc Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 $ echo $?
 1
 }}}

 Again, no errors are emitted, but compilation definitely fails, since no
 `.hi` or `.o` files are emitted, and you get an error return code of 1.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13642#comment:1
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