Re: [Caml-list] Teaching bottomline, part 3: what should improve.

[skaller <skaller@users.sourceforge.net>]

On Tue, 2007-05-22 at 18:10 -0400, David Teller wrote:

> * Error messages of the type system are somewhat obscure. The reflex of
> many students is "OCaml wants it to be of type XXX", rather than "there
> is a contradiction in what I wrote". It would be nice if there was a way
> to ask OCaml to display additional information on type errors.

This is a long standing peeve of mine. Lets face it: Ocaml just lies.
If it has inferred a type, then finds a contradiction, it should
report both the location of the contradication AND all of the source
lines that contributed to the inference.

I understand that is may be hard, if not impossible, to implement,
as it would require a unification engine that could manage
source references in parallel with deductions .. still the information
IS available originally.

I bet this would be an interesting and valuable PhD project,
and, IMHO, without it type inferencing languages are useless
in industry. Type errors in Ocaml code are very common for the
simple reason they're just about the only error you can make :)


-- 
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net