I think this is quite a reasonable suggestion. Edward
Excerpts from Evan Laforge's message of 2015-10-23 19:48:07 -0700: > Here's a typical simple type error from GHC: > > Derive/Call/India/Pakhawaj.hs:142:62: > Couldn't match type ‘Text’ with ‘(a1, Syllable)’ > Expected type: [([(a1, Syllable)], [Sequence Bol])] > Actual type: [([Syllable], [Sequence Bol])] > Relevant bindings include > syllables :: [(a1, Syllable)] > (bound at Derive/Call/India/Pakhawaj.hs:141:16) > best_match :: [(a1, Syllable)] > -> Maybe (Int, ([(a1, Syllable)], [(a1, Sequence Bol)])) > (bound at Derive/Call/India/Pakhawaj.hs:141:5) > In the second argument of ‘mapMaybe’, namely ‘all_bols’ > In the second argument of ‘($)’, namely > ‘mapMaybe (match_bols syllables) all_bols’ > > I've been having more trouble than usual reading GHC's errors, and I > finally spent some time to think about it. The problem is that this new > "relevant bindings include" section gets in between the expected and actual > types (I still don't like that wording but I've gotten used to it), which > is the most critical part, and the location context, which is second most > critical. Notice the same effect in the previous sentence :) After I see > a type error the next thing I want to see is the where it happened, so I > have to skip over the bindings, which can be long and complicated. Then I > usually know what to do, and only look into the bindings if something more > complicated is going on, like wonky inference. So how about reordering the > message: > > Derive/Call/India/Pakhawaj.hs:142:62: > Couldn't match type ‘Text’ with ‘(a1, Syllable)’ > Expected type: [([(a1, Syllable)], [Sequence Bol])] > Actual type: [([Syllable], [Sequence Bol])] > In the second argument of ‘mapMaybe’, namely ‘all_bols’ > In the second argument of ‘($)’, namely > ‘mapMaybe (match_bols syllables) all_bols’ > Relevant bindings include > syllables :: [(a1, Syllable)] > (bound at Derive/Call/India/Pakhawaj.hs:141:16) > best_match :: [(a1, Syllable)] > -> Maybe (Int, ([(a1, Syllable)], [(a1, Sequence Bol)])) > (bound at Derive/Call/India/Pakhawaj.hs:141:5) > > After this, why not go one step further and set off the various sections > visibly to make it easier to scan. The context section can also be really > long if it gets an entire do block or record: > > Derive/Call/India/Pakhawaj.hs:142:62: > * Couldn't match type ‘Text’ with ‘(a1, Syllable)’ > Expected type: [([(a1, Syllable)], [Sequence Bol])] > Actual type: [([Syllable], [Sequence Bol])] > * In the second argument of ‘mapMaybe’, namely ‘all_bols’ > In the second argument of ‘($)’, namely > ‘mapMaybe (match_bols syllables) all_bols’ > * Relevant bindings include > syllables :: [(a1, Syllable)] > (bound at Derive/Call/India/Pakhawaj.hs:141:16) > best_match :: [(a1, Syllable)] > -> Maybe (Int, ([(a1, Syllable)], [(a1, Sequence Bol)])) > (bound at Derive/Call/India/Pakhawaj.hs:141:5) > > Or alternately, taking up a bit more vertical space: > > Derive/Call/India/Pakhawaj.hs:142:62: > Couldn't match type ‘Text’ with ‘(a1, Syllable)’ > Expected type: [([(a1, Syllable)], [Sequence Bol])] > Actual type: [([Syllable], [Sequence Bol])] _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
