[Haskell-cafe] Human-friendly compiler errors for GHC

Isaac Dupree isaacdupree at charter.net
Sun Jul 13 06:11:22 EDT 2008

wren ng thornton wrote:
> Max Bolingbroke wrote:
>> Agreed: I've implemented this too. I've also added fuzzy matching to
>> package search:
>> """
>> $ stage2/ghc-inplace --make ../Test1.hs
>> ../Test1.hs:3:7:
>>     Could not find module `Data.Lost':
>>       Use -v to see a list of the files searched for.
>>       Maybe you meant `Data.List'
>> $ stage2/ghc-inplace --make ../Test2.hs
>> [1 of 1] Compiling Main             ( ../Test2.hs, ../Test2.o )
>> ../Test2.hs:7:14:
>>     Not in scope: `isSpace'
>>     Maybe you meant `Char.isSpace'
>> """
> In terms of making error messages more helpful, I don't find general 
> typos are much of an issue, but this part would be really nice! I've 
> always been annoyed that GHC just says "no" rather than offering 
> suggestions (-v is rarely helpful), especially since it knows about what 
> modules are installed et al.

It sounds like it only searches for modules you've imported (after all 
they might've been brought into scope with an as-clause, and ghc has no 
business poking in un-imported modules), but perhaps since in GHCi all 
modules are in scope (under their original names -- in addition to any 
imports in an interpreted file), it (ghci) searches all modules then?

If I want a "perhaps you meant to import" message, I want it to be a 
*complete* listing of modules available that export that symbol, both 
local ones and library ones, ideally :-)  (certainly don't want a 
recommendation to import e.g. List without at least an equal 
recommendation of Data.List...)


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