Am Donnerstag, 5. März 2009 19:13 schrieb Francesco Bochicchio:
2009/3/4 7stud
Here are my top three:
...
3) Not putting parentheses around arguments of the form x:xs
dosomething x:xs = head xs
I have a variation here:
function [] = ... function [x:xs] = ...
Another of mine is the classical:
print function arguments -- or variations
but I finally learned to use '$' here .
In all three cases, the error messages don't help spot the problem.
At least they give a source position, so you know where to look. But yes, "parse error" is not very specific.
I think that part of the problem is that haskell syntax is powerful but
terse, and therefore is not easy for a compiler to guess the intentions in the programmers. For instance, in any other language the expression 'map f' would give the error "missing second parameter", while in haskell could be a partial function application.
However, some of ghc messages could probably be made more 'beginners-friendly'.
Create a ticket if you encounter a particularly unhelpful error message. If you can suggest a better message, all the better.
Ciao --------- FB
Cheers, Daniel