[GHC] #9872: Runing type functions is too slow

[GHC]

#9872: Runing type functions is too slow
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              Reporter:  simonpj     |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Replying to [comment:3 goldfire]:
 > This all begs a question I've wondered several times: Flattening in the
 solver is great when we have bits of a type that are unknown, like `F
 (Int, a)`. But, it seems like an awful lot of work to do when a type is
 fully known, such as `F Bool`. In the latter case, is there a reason we
 don't use `normaliseType`? It would seem to me that this all would get
 more efficient if we just called `normaliseType` as an early step in the
 process, say in `flattenFamApp`.

 Reasonable question.  But if we had
 {{{
    Eq (F (P Q R)
          (G (H (F (G (H a Int))))))
 }}}
 there's a risk of trying to normalise at the outer level, and then at
 every inner level, which would not be very clever.  I'll think about this
 a bit more.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9872#comment:6>
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