I created a ticket for the feature request:
Ticket #7870
Teachers, newbies and people working in Industry: Please push it!
2013/4/24 Alberto G. Corona
Maybe it is possible to do something In a google summer of code. Nothing as sophisticated as the Helium paper ("Scripting the Type Inference Process", but maybe a partial implementation of the techniques mentioned, so that the development can be enhanced in the future.
Maybe some kind of library that permits postprocessing of GHC errors and/or the identification of points in the current type checker where some kind of rules can be defined by the programmer can be the first step.
2013/4/23 Brent Yorgey
On Tue, Apr 23, 2013 at 12:49:59PM +0200, Alberto G. Corona wrote:
Hi
I ever was worried about the barrier that the complexity of the Haskell errors impose to users of DSLs. Many DSLs look so simple that even someone without knowledge of Haskell can make use of them for some domains.
However when the program is compiled then al the monsters of the deep appear in the surface: polymorphisms, undefined instances, type errors reported in a line produced by a type assumption in another, etc. This is a problem for an industrial use of Haskell in the large scale. For obvious reasons.
Indeed. For example, in my experience this is a big problem for diagrams.
The question: Is it possible to develop a GHC extension that attach (or prepend) such an explanation to the ghc error?
Or any other alternative that carry out the same functionality.
Surely it is possible. I have wanted this too. I guess the majority of the work would just be in coming up with a good, general design which is useful but not too difficult to implement. If anyone wanted to undertake such a project I would be happy to contribute some ideas.
-Brent
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-- Alberto.
-- Alberto.