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Re: [Axiom-developer] Unions in Spad


From: Stephen Wilson
Subject: Re: [Axiom-developer] Unions in Spad
Date: 11 Jul 2007 12:22:15 -0400
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.4

Hello Waldek,

Waldek Hebisch <address@hidden> writes:

> I think it is better to catch such errors on a post-parsing stage.
> Why this may matter: syntax errors frequently leave parser in a
> confused state, making hard to detect other errors.  Also for users
> is seem easier to have simple syntax + set of semantic constraints
> than to encode constraints in syntax.

My personal preference is for strict syntax constraints, with a syntax
error being a hard error.  Main reasons being that to continue and
process syntactically invalid input is for the sole purpose of generating
additional error messages.  I feel users would not mind having a
single accurate error message vs. wading through a pile of possibly
nonsensical reports.  I find this approach more useful especially when
the language has an interpreter (which would be very nice to have for
Spad). 

Semantic errors are just as likely to leave a type-checker or other
analysis phase in a confused state.

Im not sure how simple syntax vs. strict semantic constraints makes
the users life any easier.  They still need to play by the rules,
grammatical or not.

Just my 2 cents.


Take care,
Steve





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