[antlr-interest] Using antlr to retreive logical expressions

[Bart Kiers]

Only that tutorial is based on ANTLR v2.7, whose syntax differs
considerably from the most recent ANTLR version (3.4).

Regards,

Bart.


On Thu, Mar 1, 2012 at 8:12 PM, Kunal Naik <kunal.a.naik at gmail.com> wrote:

> Hi Miguel,
>
> I think this blog post might be beneficial to you:
>
> http://www.alittlemadness.com/2006/06/05/antlr-by-example-part-1-the-language/
> In part 4 he explains the process of writing a tree grammar where you can
> inject your code that can evaluate your expressions.
>
> HTH,
> Kunal
>
> On Thu, Mar 1, 2012 at 1:31 PM, Miguel Almeida <migueldealmeida at gmail.com
> >wrote:
>
> > Dear all,
> >
> > I need to parse and evaluate expressions which are in the format:
> > - x eq 1 && y eq 10
> > - (x lt 10 && x gt 1) || x eq -1
> >
> > I have the evaluator part working (ie, I have code that evaluates all the
> > gt/lt/eq/neq expressions. All I need is the part that breaks the clause
> > into these expressions and then applies the logical and/or's
> >
> > I saw a recommendation on ANTLR to do this. My idea is to:
> > 1) Build a tree
> > 2) Execute the leafs using my already existing code (eg, replace "1 eq
> 10"
> > with false)
> > 3) Execute a method that then applies the logical operation to get the
> > result of the tree
> >
> > While I've spend the last couple of days reading things about ANTLR, I am
> > kind of lost at the moment: I can't seem to be able to get a tree
> structure
> > whose tokens hold either the && and || or the complete expressions.
> >
> > My current grammar is [1]. An example test case is [2]
> > - If I omit the | ' ' from the ID, "x eq 1" will be 3 tokens instead of
> the
> > one token I need
> > - If I leave it there, then for example this "1 eq 1 && (bb eq 1)"
> > expression won't work (No viable alternative at input '(' )
> >
> >
> > Could you shed some light on what could be wrong?
> >
> > [1]
> > grammar Logic;
> >
> > options {
> >  output = AST;
> > }
> >
> > tokens {
> >  AND = '&&';
> >  OR  = '||';
> > }
> >
> > // parser/production rules start with a lower case letter
> > parse
> >  :  expression EOF!    // omit the EOF token
> >  ;
> >
> > expression
> >  :  implication
> >  ;
> >
> > implication
> >  :  or ('->'^ or)*    // make `->` the root
> >  ;
> >
> > or
> >  :  and ('||'^ and)*    // make `||` the root
> >  ;
> >
> > and
> >  :  not ('&&'^ not)*      // make `&&` the root
> >  ;
> >
> > not
> >  :  '~'^ atom    // make `~` the root
> >  |  atom
> >  ;
> >
> > atom
> >  :  ID+
> >  |  '('! expression ')'!    // omit both `(` and `)`
> >  ;
> >
> >
> > // lexer/terminal rules start with an upper case letter
> > ID
> >  :
> >    (
> >    'a'..'z'
> >    | 'A'..'Z'
> >    | '0'..'9'
> >    | ' '
> >  )+
> >  ;
> >
> > Space : (' ' | '\t' | '\r' | '\n')+ {$channel=HIDDEN;};
> >
> >
> >
> > [2] Example test case
> >    @Test
> >    public void complexAndOr() throws RecognitionException{
> >        // the expression
> >        String src = "(1 eq 1 && 2 eq 2) || 3 eq 3";
> >
> >        // create a lexer & parser
> >        LogicLexer lexer = new LogicLexer(new ANTLRStringStream(src));
> >        LogicParser parser = new LogicParser(new
> CommonTokenStream(lexer));
> >
> >        // invoke the entry point of the parser (the parse() method) and
> > get the AST
> >        CommonTree tree = (CommonTree)parser.parse().getTree();
> >
> >        assertEquals("||",tree.getText());
> >        Tree child1 = tree.getChild(0);
> >        assertEquals("&&",or.getText());
> >        assertEquals("1 eq 1",child1.getChild(0));
> >        assertEquals("2 eq 2",child1.getChild(1));
> >        assertEquals("3 eq 3",tree.getChild(1).getText());
> >    }
> >
> > Thank you,
> >
> > Miguel
> >
> > List: http://www.antlr.org/mailman/listinfo/antlr-interest
> > Unsubscribe:
> > http://www.antlr.org/mailman/options/antlr-interest/your-email-address
> >
>
> List: http://www.antlr.org/mailman/listinfo/antlr-interest
> Unsubscribe:
> http://www.antlr.org/mailman/options/antlr-interest/your-email-address
>