[GHC] #10711: Defining mapM_ in terms of traverse_ causes substantial blow-up in ByteCodeAsm

[GHC]

#10711: Defining mapM_ in terms of traverse_ causes substantial blow-up in
ByteCodeAsm
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        Reporter:  bgamari           |                   Owner:  bgamari
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |               Test Case:  ghcirun004
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by nomeata):

 Another factoid:
  * It does not help to implement `<$` (used by the default implementation
 of `*>`) manually.
  * It does not help to implement `<*>` manually
  * So `a1 *> a2   = (id <$ a1) <*> a2` indeed seems to be the root of the
 problem.

 Do we need to educate people to write `(*>) == (>>)` if they write `(<*>)
 = ap`?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10711#comment:8>
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