|VB/VBA: Creating list of variables and parsing statements email@example.com (Howard Kaikow) (2000-11-26)|
|Re: VB/VBA: Creating list of variables and parsing statements firstname.lastname@example.org (2000-11-30)|
|Re: VB/VBA: Creating list of variables and parsing statements email@example.com (Scott Nicol) (2000-12-01)|
|Re: VB/VBA: Creating list of variables and parsing statements firstname.lastname@example.org (2000-12-03)|
|From:||Scott Nicol <email@example.com>|
|Date:||1 Dec 2000 13:17:59 -0500|
|Posted-Date:||01 Dec 2000 13:17:59 EST|
> Finding and parsing declarations of variables is not very
I agree with you on this point, at least for global- and module-level
> If you want to parse statements, I
> suggest that you start with an existing parser or syntax for any (not
> too sophisticated) language, and add the VB/VBA extensions
VB is a very difficult language to parse correctly. It's not as bad
as Fortran, but it makes a valiant attempt. There are silly things
- 3(!) pass compilation: global/module variables and
procedures, procedure variables, statements.
Variables declared anywhere with a procedure are
accessible anywhere within a procure, so you have to
parse all variables first (or patch up later, but
this can make things more difficult).
- reserved words that are reserved only in certain
contexts (i.e. "access", "append" and "binary"
are reserved words in an Open statement, but are
identifiers in most other contexts).
- scoping rules that are _very_ complicated. It
took me a few months to get these correct.
- parenthesis are significant, and not just for
evaluation order. Parenthesis also remove
reference, so you can force pass-by-value when
a procedure wants pass-by-reference.
- lots of places where more-than-one lookahead is
needed. End vs. End If, End While, etc are
fairly easy to fix in the scanner, but the
"." notation when mixed with arrays is a bit more
difficult. For instance, save your work (in all
applications if you are using Win95/98/me), then
enter the following into VB's editor:
redim x(1 to 5).y(2)
When you press enter, VB will crash, because MS
didn't handle the (complicated) parsing of arrays
within types in redim statements correctly. Yes,
I realize the line is a syntax error.
In general, to do it right, you are going to have lots of interaction
between the parser and the scanner. This makes using Lex/YACC tricky.
To top it off, there is no language spec. The official "Language
Reference" is a start, but it is incomplete, inaccurate, and poorly
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