[DGD] Parse_string confusion

[Noah Lee Gibbs]

On Fri, 18 Jan 2002, Erwin Harte wrote:

> On Fri, Jan 18, 2002 at 01:27:03AM -0800, Noah Lee Gibbs wrote:
> > return !!parse_string("regstring = /[^A-Z]+/\n\nfull: regstring\n", str);

  The line above, the one with the return, gives literally the complete
grammar.  With the "\n" characters expanded, it looks like this:

regstring = /[^A-Z]+/

full: regstring

That's not what I'd like in a perfect world.  What I'd like in a perfect
world is to use it to find out if the string's alphabetic, like this:

regstring = /[A-Za-z]+/

full: regstring

That'd mean that the grammar parsed iff it consisted of a single string
made only of the upper- or lower-case letters with no digits, no spaces
and no punctuation characters.

Input: "snowball" would give a result of ({ "snowball" }), while the input
"Haxx0r", which contains a digit, would fail to parse.  The !! in front of
the parse_string call converts to boolean -- if it parses, the function
returns true.  If it doesn't parse, the function returns false.  In the
original example (which DGD accepts) it will return true for a string
*not* containing any uppercase letters -- the token was /[^A-Z]+/.  But I
used that example because, unlike the example I wrote above with the token
/[A-Za-z]+/, parse_string didn't give an error trying to understand the
grammar I gave it.  The version in the line with the return above is
accepted by parse_string as a valid grammar.  Changing the section of it
in slashes to any of the things I listed as "won't work" means that
parse_string gives an error, claiming it's not a valid grammar.  I could
certainly believe I've made some mistake in writing the grammar, but then
parse_string must be only sometimes noticing that mistake.

> Can you give some combinations of:
> 
> - Complete grammar used.
> - Input given.
> - Output expected.
> 
> Because I'm not quite sure what you're trying to do here. :)
> 
> Erwin.
> -- 
> Erwin Harte <harte at xs4all.nl>
> _________________________________________________________________
> List config page:  http://list.imaginary.com/mailman/listinfo/dgd
> 

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