Re: [Haskell-cafe] How to debug GHC

Thanks, Ketil, your suggestion really helped me ! Thanks to Claus for the tips ! On 4/26/05, Ketil Malde wrote:

"Claus Reinke" writes:

...

no direct answer to your question, but a general comment on the original problem (speaking from bad experience;-): things like "head" have no place in a Haskell program of any non-trivial size, because of their useless error messages.

I must say I liked John Meacham's description of his "magic underscore". My solution to this problem is redefining the troublesome functions as cpp macros, e.g:

#define BUG(C_,M_) (error ("Program error - '"++C_++"' failed: "++M_++". Location: '"++__FILE__++"' line "++show __LINE__)) #define head (\xs -> case xs of { (x:_) -> x ; _ -> BUG("head","empty list")})

Ideally, I think something like this should be the default behavior for these functions.

-kzm

PS: If anybody wants, I can mail my additional cpp definitions for 'head', 'at' (array indexing, I couldn't work out how to redefine the bang), 'read' and 'fromJust'. -- If I haven't seen further, it is by standing in the footprints of giants

-- ________________________________ Monique Louise B.Monteiro Msc Student in Computer Science Center of Informatics Federal University of Pernambuco