[GHC] #15646: ghci takes super long time to find the type of large fractional number

[GHC]

#15646: ghci takes super long time to find the type of large fractional number
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        Reporter:  Johannkokos       |                Owner:
                                     |  JulianLeviston
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  GHCi              |              Version:  8.4.3
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #5692             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by JulianLeviston):

 I've been trying to move `mkRational`, but it doesn't seem to make any
 sense to put it into base itself... (ie `GHC.Real`). If we put it into
 there, won't it expose it to base? It seems like a strange thing to do, to
 me.

 The reason it needs to be exposed *somewhere* is that it's looked up
 globally by id, here: https://github.com/JulianLeviston/ghc/pull/1/files
 #diff-116aa33edfc74c0dc68e471f30ac63d5R101 but perhaps we don't actually
 need to look it up there? I'm pretty lost.


 Here's the code... it's the bottom of the `dsLit` function in
 `compiler/deSugar/Matchlit.hs`:
 {{{
     HsRat _ fl _     -> case fl of
                           FL { fl_signi = fl_signi, fl_exp = fl_exp } ->
 do
                             mkRational <- dsLookupGlobalId mkRationalName
                             litI <- mkIntegerExpr fl_signi
                             litE <- mkIntegerExpr fl_exp
                             return ((Var mkRational) `App` litI `App`
 litE)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15646#comment:63>
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