[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:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by osa1):

 Could you submit your patch to Phabricator? It's really hard to review it
 this way.

 I haven't looked at the patch in details yet, but the desugaring in
 comment:41 is not right. We want to avoid building a rational in compile
 time (the `Integer` components of `Rational` is what's taking all the
 time), but that's what you're doing in the code in comment:41 (in
 `readRational`). See comment:24 for how we want to desugar this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15646#comment:42>
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