Re: [GHC] #15633: Type-checker plugins aren't loaded in GHCi 8.6.1

14 Sep 2018

      #15633: Type-checker plugins aren't loaded in GHCi 8.6.1
-------------------------------------+-------------------------------------
        Reporter:  phadej            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.6.1-beta1
      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 darchon):

 To elaborate further

 Loading:
 {{{
 {-# LANGUAGE DataKinds, TypeOperators #-}
 module Test where

 import Data.Proxy
 import GHC.TypeLits

 p1 :: Proxy a -> Proxy b -> Proxy (a + b) -> Proxy (b + a)
 p1 _ _ = id
 }}}

 without the normalisation plugin gives:

 {{{
 $ ghci Test.hs
 GHCi, version 8.6.0.20180907: http://www.haskell.org/ghc/  :? for help
 Loaded package environment from /home/christiaan/devel/clash-compiler
 /clash-prelude/.ghc.environment.x86_64-linux-8.6.0.20180907
 [1 of 1] Compiling Test             ( Test.hs, interpreted )

 Test.hs:8:10: error:
     • Couldn't match type ‘a + b’ with ‘b + a’
       Expected type: Proxy (a + b) -> Proxy (b + a)
         Actual type: Proxy (b + a) -> Proxy (b + a)
       NB: ‘+’ is a non-injective type family
     • In the expression: id
       In an equation for ‘p1’: p1 _ _ = id
     • Relevant bindings include
         p1 :: Proxy a -> Proxy b -> Proxy (a + b) -> Proxy (b + a)
           (bound at Test.hs:8:1)
   |
 8 | p1 _ _ = id
   |          ^^
 Failed, no modules loaded.
 }}}

 and of course with the normalisation plugin gives:

 {{{
 $ ghci -fplugin=GHC.TypeLits.Normalise Test.hs
 GHCi, version 8.6.0.20180907: http://www.haskell.org/ghc/  :? for help
 Loaded package environment from /home/christiaan/devel/clash-compiler
 /clash-prelude/.ghc.environment.x86_64-linux-8.6.0.20180907
 [1 of 1] Compiling Test             ( Test.hs, interpreted )
 Ok, one module loaded.
 *Test>
 }}}

 However, the following session in GHCi doesn't seem to work:

 {{{
 $ ghci -fplugin=GHC.TypeLits.Normalise -XDataKinds -XTypeOperators
 GHCi, version 8.6.0.20180907: http://www.haskell.org/ghc/  :? for help
 Loaded package environment from /home/christiaan/devel/clash-compiler
 /clash-prelude/.ghc.environment.x86_64-linux-8.6.0.20180907
 Prelude> import Data.Proxy
 Prelude Data.Proxy> import GHC.TypeLits
 Prelude Data.Proxy GHC.TypeLits> :{
 Prelude Data.Proxy GHC.TypeLits| p1 :: Proxy a -> Proxy b -> Proxy (a + b)
 -> Proxy (b + a)
 Prelude Data.Proxy GHC.TypeLits| p1 _ _ = id
 Prelude Data.Proxy GHC.TypeLits| :}

 <interactive>:5:10: error:
     • Couldn't match type ‘a + b’ with ‘b + a’
       Expected type: Proxy (a + b) -> Proxy (b + a)
         Actual type: Proxy (b + a) -> Proxy (b + a)
       NB: ‘+’ is a non-injective type family
     • In the expression: id
       In an equation for ‘p1’: p1 _ _ = id
     • Relevant bindings include
         p1 :: Proxy a -> Proxy b -> Proxy (a + b) -> Proxy (b + a)
           (bound at <interactive>:5:1)
 Prelude Data.Proxy GHC.TypeLits>
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15633#comment:2
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