Changes between Initial Version and Version 2 of Ticket #1549


Ignore:
Timestamp:
Aug 9, 2007 2:38:08 PM (7 years ago)
Author:
int-e
Comment:

Thank you.

The connection that I hadn't made is that type inference (in particular, choosing an instance to use for type classes for a monotype) and constraint simplification (which affects polymorphic types) are really the same thing.

Once that misconception is resolved the behaviour is just as expected. The documentation could be clearer about the fact that allowing overlapping instances does not change the behaviour for the case when none are present though.

Maybe inserting "This flag does not change ghc's behaviour when no overlapping instances are present." after "The -fallow-overlapping-instances flag instructs GHC to allow more than one instance to match, provided there is a most specific one." would clear that up?

Bertram

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  • Ticket #1549

    • Property Status changed from new to reopened
    • Property Component changed from Compiler (Type checker) to Documentation
    • Property Priority changed from normal to low
    • Property Type changed from bug to proposal
    • Property Severity changed from normal to trivial
  • Ticket #1549 – Description

    initial v2  
     1Insert "This flag does not change ghc's behaviour when no verlapping instances are present." after "The -fallow-overlapping-instances lag instructs GHC to allow more than one instance to match, provided here is a most specific one." in http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html#instance-overlap 
     2 
     3(old description follows for reference) 
     4 
    15The code below derives two different type signatures for the same function in two different modules. 
    26