Changes between Initial Version and Version 2 of Ticket #4917


Ignore:
Timestamp:
Jan 25, 2011 11:08:19 AM (5 years ago)
Author:
simonpj
Comment:

Very good point, thank you. Fixed by

Tue Jan 25 11:01:12 GMT 2011  [email protected]
  * Fix Trac #4917: try a bit harder to unify on-the-fly
  
  This is generally a modest improvement but, more important,
  it fixes a "unify-under-forall" problem.  See Note [Avoid deferring].
  
  There's still a lurking unsatisfactory-ness in that we can't
  defer arbitrary constraints that are trapped under a forall.

    M ./compiler/typecheck/TcUnify.lhs -8 +28

Ian, please merge.

Simon

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  • Ticket #4917

    • Property Status changed from new to merge
    • Property Test Case changed from to typecheck/should_compile/T4917
    • Property Component changed from Compiler to Compiler (Type checker)
  • Ticket #4917 – Description

    initial v2  
    66
    77The type error message is
    8 
     8{{{
    99ghc7rankn.hs:23:20:
    1010    Couldn't match expected type `forall a'1.
     
    1919    In the first argument of `mcata', namely `f'
    2020    In the first argument of `f', namely `(mcata f)'
     21}}}