[GHC] #8318: GHC does not infer type of `tagToEnum#` expression

[GHC]

#8318: GHC does not infer type of `tagToEnum#` expression
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        Reporter:  jstolarek                  |            Owner:
            Type:  bug                        |           Status:  new
        Priority:  normal                     |        Milestone:
       Component:  Compiler                   |          Version:  7.7
      Resolution:                             |         Keywords:
Operating System:  Unknown/Multiple           |     Architecture:
 Type of failure:  GHC rejects valid program  |  Unknown/Multiple
       Test Case:                             |       Difficulty:  Unknown
        Blocking:                             |       Blocked By:
                                              |  Related Tickets:
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Comment (by jstolarek):

 Compiling this program:
 {{{
 {-# LANGUAGE MagicHash, UnboxedTuples #-}
 module TTE where

 import GHC.Prim
 import GHC.Base

 g :: IO Bool
 g = IO $ \s# -> (# s#, tagToEnum# 1# #)
 }}}
 produces:
 {{{
 [1 of 1] Compiling TTE              ( tte.hs, tte.o )

 tte.hs:11:24:
     Bad call to tagToEnum# at type a_azp
       Specify the type by giving a type signature
       e.g. (tagToEnum# x) :: Bool
     In the expression: tagToEnum# 1#
     In the expression: (# s#, tagToEnum# 1# #)
     In the second argument of ‛($)’, namely
       ‛\ s# -> (# s#, tagToEnum# 1# #)
 }}}
 So the informative error message is already somewhere in the compiler. I
 wonder why don't we infer the type here? After all the error message
 clearly states what type is necessary.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8318#comment:1>
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