Pierre Weis wrote:

> Clearly, there is something wrong now! We may remark that the error
> message is not that clear, but this is a minor point, since error
> messages are never clear enough anyway!

	This is not a 'minor' point, but the most significant obstacle
in the way of adoption of languages (like ocaml) that do a lot of type
inference. Incomprehensible -- indeed plain wrong -- error messages
crop up regularly with ocaml, and vie with the kind of gibberish
errors instantiating C++ templates usually give for 
'most obscuficated error message' competition :-)

	The recent addition of better error messages in the case
of missing cases of matches has been a _major_ improvement IMHO:
it has already saved me significant time; since I often enhance
the set of cases of a variant, and need to chase down every
match and update it.

	I'm not using -modern mode and the main reason is the scary
error messages. Even the polymorphic variants are scary, since one
looses the ability to 'spell check' variant tags. I actually tried
to take a fairly large, fundamental, type in Vyper (the type of most
language terms and runtime values) and use polymorphic variants
to classify them (the classes overlap, which ordinary variants
cannot handle), and gave up, because I couldn't understand the
error messages.

	Recent discussions in the Python types-SIG concerning
type inference showed a strong indication (mainly from ex-ML 
users) NOT to use any kind of type inference that could lead
to incomprehensible error messages.

	I personally use errors to drive development.
I expect a compiler to tell me the line that next needs editing.
Ocaml is fairly good here now, but I still cringe in fear
when i get too incompatible object types and pages of
method signatures the compiler claims are different.

Why can't it tell me the differences more often?
I does well sometimes telling me that one sig has a method the
other lacks. 

-- 
John (Max) Skaller, mailto:skaller@maxtal.com.au
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
checkout Vyper http://Vyper.sourceforge.net
download Interscript http://Interscript.sourceforge.net