|Please comment on my first parser firstname.lastname@example.org (Bart Vandewoestyne) (2012-10-10)|
|Re: Please comment on my first parser email@example.com (Jim Patchell) (2012-10-13)|
|From:||Jim Patchell <firstname.lastname@example.org>|
|Date:||Sat, 13 Oct 2012 20:50:14 -0700 (PDT)|
|Posted-Date:||14 Oct 2012 17:35:18 EDT|
On Wednesday, October 10, 2012 6:28:33 AM UTC-7, Bart Vandewoestyne wrote:
> [ a parser]
Well, it is nice to know there are other parser/compiler hobbyists out there besides myself.
I think your grammar has a few problems in it, however.
You start off with:
and then later on you have...
: expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression
If you BREAK production is some sort of a program flow control you could write
BREAK + BREAK
as a legal arithmetic_expresion.
I don't thing you meant that.
This is how I would start your grammar:
program: statements, eof //this means we have a list of statements followed by end of file
statements: statment //this is a left recursion rule for
| statements, statement //making a list of statements
assignments: lvalue EQUALS expression
expression: expression MUL addexpr
| expression DIV addexpr
addexpr: addexpr PLUS urnary
| addexpr MINUS urnary
urnary : primary
| MINUS primary
| LPAREN, expression, RPARAN
I sure hope I didn't make any grievous errors in that. There is a lot to be filled in also, Obviously.
Also, your grammar looks like it was written for either yacc or bison. Those are OK, but, there are better parser generators out there, and by better, I mean easier to use.
Take a look at Anagram ( http://www.parsifalsoft.com/ )
and LRstar (http://www.compilerware.com) seems to be offline at the moment :-(
and ANTLR ( http://www.antlr.org/ )
I haven't actually really tried ANTLR yet, but it is a very well documented package. Anagram and LRstar are my two fav LALR(1) parser generators. LRstar will even do LALR(k). ANTLR generates the so called LL(k) parsers.
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