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From: Philipp Kempgen on 12 Aug 2010 14:04
Hi,

I'm looking for a parser which can be fed with some (A)BNF-style rules.

Gave TreeTop a try
---cut---------------------------------------------------------
grammar MathGrammar
rule additive
multitive '+' additive / multitive
end
rule multitive
primary '*' multitive / primary
end
rule primary
'(' additive ')' / number
end
rule number
[1-9] [0-9]*
end
end
---cut---------------------------------------------------------

as well as GhostWheel
---cut---------------------------------------------------------
MathParser = GhostWheel.build_parser {

rule( :additive , alt( :multitive,
seq( :multitive, '+', :additive )
))
rule( :multitive , alt( seq( :primary, '*', :multitive ),
:primary
))
rule( :primary , alt( seq( '(', :additive, ')' ),
:number
))
rule( :number , seq( /[1-9]/ , zplus( /0-9/ ) ))

parser( :main, seq(:additive, eof()) )
}
---cut---------------------------------------------------------

'1+1' parses fine.
However when I change the definition of "additive" from
multitive '+' additive / multitive
to
multitive / multitive '+' additive
it fails to parse.

Is this a problem with packrat/PEG parsers in general?
If so, which parser is more appropriate?
It should hand back a parse tree.

Memory consumption is not an issue.

Regards,
Philipp

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