[GHC] #4321: Unexpected stack overflow prevented by superfluous type annotation

[GHC]

#4321: Unexpected stack overflow prevented by superfluous type annotation
-------------------------------+--------------------------------------------
  Reporter:  bjpop             |          Owner:                  
      Type:  bug               |         Status:  new             
  Priority:  normal            |      Milestone:  7.4.1           
 Component:  Compiler          |        Version:  6.13            
Resolution:                    |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:                  
  Testcase:  T4321             |      Blockedby:                  
  Blocking:                    |        Related:                  
-------------------------------+--------------------------------------------
Changes (by michalt):

  * status:  closed => new
  * resolution:  fixed =>


Comment:

 Unfortunately the current HEAD fails T4321 for me due to stack overflow.
 It
 seems that the problem is similar -- ```sum``` doesn't get inlined by
 current
 HEAD whereas GHC 7.4 does inline it.

 Maybe I'm missing something, but it seems to me that an easy fix would be
 to
 slightly modify the definition of ```sum```:
 {{{
 sum     l       = sum' l 0
   where
     sum' []     a = a
     sum' (x:xs) a = sum' xs (a+x)
 }}}
 by making ```sum'``` strict in the second argument or by defining it as
 ```foldl' (+) 0```. Is there any reason not to do that?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4321#comment:16>
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