Recursive descent parser generator: Difference between revisions

It can't handle newlines as part of the grammar, the error checking is fairly limited and the error reporting is basically non-existent, but the parser it generates (not shown below) is human readable.

 

#include <fstream>

#include <map>

#include <regex>

using namespace std;

 

 

int main(int argc, char **argv) {

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

}

 

Example grammar:

 

I've therefore applied this parser to the expression designated by the task, which only involves binary expressions and identifiers, and written a separate routine to convert the resulting AST into three-address code.

 

import (

last = i

}

 

{{out}}

Implementation:

 

 

inlocale=: 4 :0 L:0

 

emit=: smoutput

 

Task example:

 

z0001=:four*five

z0002=:one+two

z0003=:z0002*three

z0004=:z0003-z0001

 

See also https://github.com/jsoftware/general_misc/blob/master/trace.ijs for a model of the underlying parser being employed here.

=={{header|Julia}}==

The Julia compiler's own parser is a recursive descent parser, and can be used directly here.

 

function testparser(s)

 

testparser("(one + two) * three - four * five")

<pre>

$(Expr(:thunk, CodeInfo(

 

=={{header|Perl}}==

 

use strict; # https://rosettacode.org/wiki/Recursive_descent_parser_generator

@stack >= 3 or die "not enough on stack";

splice @stack, -3, 3, $stack[-2];

Running the above with no arguments uses a default grammar that will solve the specified example. It produces

the following perl script (and then runs it).

use strict; # https://rosettacode.org/wiki/Recursive_descent_parser_generator

use warnings; # WARNING: this code is generated

Rule::startsymbol();

eval { end() }; # eval because it is optional

The above script can also be run stand-alone and produces the following output.

{{out}}

</pre>

and giving this file as "arithexpr.y"

 

expr = term { '+' term <fadd> | '-' term <fsub> } .

sub fdiv { splice @stack, -3, 3, $stack[-3] / $stack[-1] }

sub begin { print "expr = $_\n" }

will produce the following

{{out}}

Technically the task is asking for code which generates something like the following, so I suppose

it would actually meet the spec if it began with <code>constant src = """</code> and ended with

{{out}}

<pre>

{{libheader|Wren-str}}

{{libheader|Wren-fmt}}

import "./fmt" for Fmt

 

}

 

 

{{out}}