Hi Christian,
this seems like a correct implementation:
...
unary
: MINUS unary -> ^(NEGATION unary)
| PLUS unary -> unary
| term
;
...
The rest strays as before, only PLUS and MINUS are new tokens.
Von: Christian Lerch [mailto:[email protected]]
Gesendet: Montag, 17. Januar 2011 13:14
An: [email protected]; Richard Andrysek
Betreff: Re: [antlr-interest] WG: Question to the tree grammer
Hi Richard,
I also had a fierce fight with unary operators, although in the context of
juxtaposition (which allows to ellide the * and write e.g. 2x instead of 2*x).
Please take a look at my small but tested grammar module that addresses this
problem.
It implements 5 precedence levels for
1. binary +, - (left-assoc)
2. multiplication (left-assoc)
3. unary +, -
4. juxtaposition interpreted as multiplication (left-assoc)
5. exponentiation (right-assoc)
A little bit anoying with this grammar is the fact, that the multiplication
implied by juxtaposition has precedence over normal multiplication.
On the other hand this can also be viewed as a feature, cause it allows you to
write e.g. 1/a b which results in the same AST as 1/(a*b)
Of course you can drop this feature altogether by simply deleting rule arithSec
and substituting all references by arithPrim.
Best wishes,
Chris
/*
Arithmetic expression grammar
with 5-level operator precedence and associativity
with handling of unary minus and unary plus
with juxtaposition mapped to multiplication
without bracketedExpr:
unnecessary parenthesis can be removed later by the code generator
*/
parser grammar ArithExpr2Parser;
options {
language = Java;
output = AST;
tokenVocab = ArithExpr2Lexer;
}
tokens {
NEG;
PAREN;
TIMES;
}
formulae: arithExpr EOF
;
arithExpr: arithTerm ( (PLUS^|MINUS^) arithTerm )*
;
arithTerm: arithFact ( (MULT^|DIV^) arithFact )*
;
arithFact: MINUS arithSec -> ^(NEG arithSec)
| PLUS! arithSec
| arithSec
;
arithSec: (arithPrim -> arithPrim)
(p=arithPrim -> ^(TIMES $arithSec $p))*
;
arithPrim: arithAtom ( POWER^ arithPrim )?
;
arithAtom: IDENT
| NUMBER
| LPAREN arithExpr RPAREN -> ^(PAREN arithExpr)
;
Am 17.01.2011 12:13, schrieb Richard Andrysek:
I want to switch from yacc. So I've looked on Videos from Scott
Stanchfield <http://vimeo.com/user566590> <http://vimeo.com/user566590> ,
especially on Part9 about a
tree grammar.
I've found a problem with an unary operator. The Interpreter in Eclipse
works fine, but the grammar tree not.
It simply can't accept things like this:
-5 - - + - 4
I've attached also my files. Is there a way, how can I ask somebody
else, than me? I assume, it is something with left/right association, is
it?
Thank you for hints
Richard
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