I've pasted an example that passes your test cases
<http://scsys.co.uk:8002/391780>. It's just one of the several possible
approaches. This one works by moving the expressions down into the
lexer, and searching for them as lexemes.
I've thought, and written in my blog, a lot on the topic of
Marpa-powered searches. But it was long ago and at that point there
wasn't much interest, so I moved on.
-- jeffrey
On 06/07/2014 10:48 PM, Steven Haryanto wrote:
Hi all,
I wonder if it's feasible to use Marpa, like regular expression, to
detect some pattern inside a string. An example of what I'm trying to
do is to extract some numeric expression from these strings:
"1+2"
"This is an expression: 1+2, and this is another 1+2+4"
"1+2 is the expression"
I want to recognize and extract 1+2 and 1+2+4 from the above. Here's
my current (and failing) attempt:
---
use MarpaX::Simple qw(gen_parser);
my $p = gen_parser(
grammar => <<'_',
lexeme default = latm => 1
:default ::= action=>::first
:start ::= answer
answer ::= expr
| expr any
| any expr action=>get1
| any expr any action=>get1
expr ::= num
| expr '+' expr
num ~ [\d]+
any ~ [\d\D]+
:discard ~ ws
ws ~ [\s]+
_
trace_terminals => 1,
trace_values => 1,
actions => {
get0 => sub { $_[1] },
get1 => sub { $_[2] },
},
);
sub check { say "Input: $_[0]"; say "Output: ", $p->($_[0]); say "=" x
20 }
check('1');
check('1 + 2');
check('1 + 2 is the expression');
check('This is an expression: 1 + 2 and another 1+2+4');
--
Regards,
Steven
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