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Re: Lexer woes
Re: Lexer woes
Wed, 24 Sep 2008 07:05:16 +0800
I was using q2c. I'll see if I can hack it to work like this.
Sometime in the future though, I think we're going to need something
better. In particular, I think it'd be really great to be able to do
command line completion, both for pspp and psppire (I understand spss
v17 does it already). So for example given a partial syntax like
if the user hits tab at this point, she'll get a list of the variable
names in the dictionary (but only those which are appropriate, ie not
scratch, string etc). Similarly, for any given command, it'd be good
to have a list of subcommands valid for that command.
But back to the current issue, parsing the K-W as three tokens, whilst
will work for the purpose of syntax verification, obviously falls down
in the bigger picture. The obvious solution would have been to allow
'-' as a valid character in the T_ID token. However this means that
suddenly get misinterpreted. But so far as I can see, there are only
a few special places in spss syntax where algebraic expressions like
that can occur (in an IF, LOOP, COMPUTE, RECODE and a few others). I
wonder if it might not be a better solution to throw the lexer into a
different mode when an expression is expected. Obviously there will
be complications (like when to switch back to non-expression mode).
On Tue, Sep 23, 2008 at 08:12:56AM -0700, Ben Pfaff wrote:
Are you parsing by hand or with q2c? If you're doing it by hand,
then you should be able to do something like this:
if (lex_token (lexer) == T_ID
&& !strcmp (lex_tokid (lexer), "K")
&& lex_look_ahead (lexer) == '-')
/* We know we're at "K-". The only acceptable
follow-on to this is "W". */
lex_force_match (lexer, '-');
if (!lex_force_match_id (lexer, "W"))
If you are using q2c, we will have to teach it a similar trick.
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