[GHC] #11994: ghci not applying defaulting when showing type

[GHC]

#11994: ghci not applying defaulting when showing type
-------------------------------------+-------------------------------------
        Reporter:  j.waldmann        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  7.10.3
      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:                    |
-------------------------------------+-------------------------------------

Comment (by aavogt):

 You could (ab)use do notation to get the defaulted type:

 {{{
 > :set +t
 Prelude> x <- return $ 1+1
 x :: Integer
 }}}

 The `it` variable is actually generalized, so the reported type is right.
 After all this works:

 {{{
 Prelude> :set +t
 Prelude> 1+1
 2
 it :: Num a => a
 Prelude> (it :: Int, it :: Double)
 (2,2.0)
 it :: (Int, Double)
 }}}

 `-XMonoLocalBinds` keeps let from being generalized in files (ie. `let x =
 1 in (x::Int,x::Integer)` becomes a type error), so I thought it might
 make a difference with respect to generalizing `it`. But it has no effect
 in ghci, not even for the `let x = ...` expression above. At least Richard
 Eisenberg seems to have said that `MonoLocalBinds` is irrelevant for ghci
 in a slightly different scenario: <https://mail.haskell.org/pipermail/ghc-
 devs/2015-August/009636.html>).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11994#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler