[Haskell-cafe] Haskell compilation errors break the complexity encapsulation on DSLs

[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