[GHC] #1454: Confusing or bug: :t and :i don't return same type

GHC trac at galois.com
Mon Jun 25 07:45:25 EDT 2007


#1454: Confusing or bug: :t and :i don't return same type
----------------------------------+-----------------------------------------
    Reporter:  iampure at gmail.com  |        Owner:         
        Type:  bug                |       Status:  new    
    Priority:  normal             |    Milestone:         
   Component:  GHCi               |      Version:  6.6.1  
    Severity:  normal             |   Resolution:         
    Keywords:                     |   Difficulty:  Unknown
          Os:  Unknown            |     Testcase:         
Architecture:  Unknown            |  
----------------------------------+-----------------------------------------
Comment (by simonpj):

 Furthermore, even quoting verbatim what GHC says in the bad case is better
 than describing in words the kind of thing it says.

 Concerning Isaac's example, this is entirely expected behaviour.  `:t`
 typechecks an '''arbitrary expression'''.  It happens to consist of a
 single variable in this case bue it could be anything at all.  E.g.
 {{{
 Prelude> :t map (* 2)
 map (* 2) :: (Num a) => [a] -> [a]
 }}}
 So GHC generates all the constraints arising from the expression and then
 abstracts over them.  There's no reason for it to keep them in the same
 order, and it doesn't.  Mabye this is what iampure (I wonder what your
 real name is) is tripping over?

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1454>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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