Changes between Initial Version and Version 1 of Ticket #3877


Ignore:
Timestamp:
Feb 12, 2010 2:51:50 PM (6 years ago)
Author:
simonpj
Comment:

Currently this is by design; see http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-overlap. Note esp the remarks at the end, which point out that the current design is not the only possible one.

So there's no great implementation challenge here; it's a design question.

Simon

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  • Ticket #3877 – Description

    initial v1  
    22
    33The code snippet is:
     4{{{
    45{- File overlap.hs -}
    56{-# OPTIONS_GHC -XOverlappingInstances -XTypeSynonymInstances #-}
     
    1112test :: Int -> String -> String
    1213test a b = show (a,b)
    13 
     14}}}
    1415
    1516The OS is :Linux 2.6.31-19-server #56-Ubuntu SMP x86_64
     
    1718
    1819The error message is:
    19 
     20{{{
    2021Glasgow Haskell Compiler, Version 6.12.1, for Haskell 98, stage 2 booted by GHC version 6.8.2
    2122Using binary package database: /usr/local/lib/ghc-6.12.1/package.conf.d/package.cache
     
    4041    In the expression: show (a, b)
    4142    In the definition of `test': test a b = show (a, b)
     43}}}
    4244
    43 
    44 
    45