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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