Created
October 29, 2012 08:56
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parser.01
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| <!doctype html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8"> | |
| <title>parser.01</title> | |
| <script src="01.parser.js"></script> | |
| </head> | |
| <body> | |
| <script> | |
| var ast = parse('2 + 3 * (5 - 6)'); | |
| console.log( JSON.stringify(ast, null, 4) ); | |
| </script> | |
| </body> | |
| </html> | |
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| var TOKEN_ADD = /^[+-]/; | |
| var TOKEN_MUL = /^[*/%]/; | |
| var TOKEN_NUMBER = /^[0-9]+(\.[0-9]+)?/; | |
| function parse(s) { | |
| var p = 0; | |
| var cur = s; | |
| var ast = parse(r_expr); | |
| if (cur) { | |
| error('End of string expected'); | |
| } | |
| return ast; | |
| // --------------------------------------------------------------------------------------------------------------- // | |
| function parse(rule) { | |
| var start = p; | |
| var ast = rule(); | |
| // ast._start = start; | |
| // ast._end = p; | |
| return ast; | |
| } | |
| function test(token) { | |
| var r = token.exec(cur); | |
| return r && r[0]; | |
| } | |
| function match(token) { | |
| var result = test(token); | |
| if (!result) { | |
| expected(token); | |
| } | |
| move(result.length); | |
| skip(); | |
| return result; | |
| } | |
| function eat(s) { | |
| var l = s.length; | |
| if ( la(l) !== s ) { | |
| expected(s); | |
| } | |
| move(l); | |
| skip(); | |
| return s; | |
| } | |
| function skip() { | |
| var r = /^\s+/.exec(cur); | |
| if (r) { | |
| move(r[0].length); | |
| } | |
| } | |
| function move(l) { | |
| l || (l = 1); | |
| p += l; | |
| cur = cur.substr(l); | |
| } | |
| function la(n) { | |
| return cur.substr(0, n || 1); | |
| } | |
| function expected(id) { | |
| error('Token ' + id + 'expected'); | |
| } | |
| function error(msg) { | |
| throw Error(msg + ' at ' + p + ' : ' + cur); | |
| } | |
| // --------------------------------------------------------------------------------------------------------------- // | |
| function r_expr() { | |
| return parse(r_add); | |
| } | |
| function r_add() { | |
| var left = parse(r_mul); | |
| if (( op = test(TOKEN_ADD) )) { | |
| match(TOKEN_ADD); | |
| return { | |
| _id: 'add', | |
| op: op, | |
| left: left, | |
| right: parse(r_add) | |
| }; | |
| } | |
| return left; | |
| } | |
| function r_mul() { | |
| var left = parse(r_primary); | |
| if (( op = test(TOKEN_MUL) )) { | |
| match(TOKEN_MUL); | |
| return { | |
| _id: 'mul', | |
| op: op, | |
| left: left, | |
| right: parse(r_mul) | |
| }; | |
| } | |
| return left; | |
| } | |
| function r_primary() { | |
| if ( la() === '(' ) { | |
| eat('('); | |
| var ast = parse(r_expr); | |
| eat(')'); | |
| return ast; | |
| } | |
| return { | |
| _id: 'number', | |
| value: +match(TOKEN_NUMBER) | |
| }; | |
| } | |
| // --------------------------------------------------------------------------------------------------------------- // | |
| } |
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