a simple example of javascript parser combinators

parse.js

function token(t) {
  return function (text) {
    if (text[0] == t)
      return text.slice(1);
    return false;
  };
}

function and() {
  var args = arguments;
  return function (text) {
    var rest = text;
    for each (arg in args) {
      rest = arg(rest);
      if (rest === false)
        return false;
    }
    return rest;
  };
}

function or() {
  var args = arguments;
  return function (text) {
    for each (arg in args) {
      var rest = arg(text);
      if (rest !== false)
        return rest;
    }
    return false;
  };
}

function oneormore(parser) {
  return function (text) {
    var rest = text;
    while (rest) {
      var r = parser(rest);
      if (r === false) {
        return rest == text ? false : rest;
      }
      rest = r;
    }
    return rest == text ? false : rest;
  };
}

function optional(parser) {
  return function (text) {
    var rest = parser(text);
    if (rest === false)
      return text;
    return rest;
  };
}

var digit = or(token("0"),
               token("1"),
               token("2"),
               token("3"),
               token("4"),
               token("5"),
               token("6"),
               token("7"),
               token("8"),
               token("9"));
var integer = oneormore(digit);
var float = or(and(optional(integer),
                   token("."),
                   integer),
               and(integer,
                   token("."),
                   optional(integer)),
               integer);
var posneg = and(optional(or(token("-"),
                             token("+"))),
                 float);
var scientific = and(posneg,
                     optional(and(or(token("e"),
                                     token("E")),
                                  posneg)));

function isNumber(text) {
  var rest = scientific(text);
  // return true only if the parser consumed the whole string
  return rest.length === 0;
}

console.log("isNumber('') => "+ isNumber('')); // false

console.log("isNumber('0') => "+ isNumber('0')); // true
console.log("isNumber('1') => "+ isNumber('1')); // true
console.log("isNumber('2') => "+ isNumber('2')); // true
console.log("isNumber('10') => "+ isNumber('10')); // true
console.log("isNumber('10a') => "+ isNumber('10a')); // false
console.log("isNumber('a') => "+ isNumber('a')); // false
console.log("isNumber('2147483648') => "+ isNumber('2147483648')); // true

console.log("isNumber('+42') => "+ isNumber('+42')); // true
console.log("isNumber('-42') => "+ isNumber('-42')); // true
console.log("isNumber('4+2') => "+ isNumber('4+2')); // false
console.log("isNumber('4-2') => "+ isNumber('4-2')); // false
console.log("isNumber('+') => "+ isNumber('+')); // false
console.log("isNumber('-') => "+ isNumber('-')); // false
console.log("isNumber('+-42') => "+ isNumber('+-42')); // false

console.log("isNumber('.42') => "+ isNumber('.42')); // true
console.log("isNumber('0.42') => "+ isNumber('0.42')); // true
console.log("isNumber('04.2') => "+ isNumber('04.2')); // true
console.log("isNumber('042.') => "+ isNumber('042.')); // true
console.log("isNumber('0.42.0') => "+ isNumber('0.42.0')); // false
console.log("isNumber('.') => "+ isNumber('.')); // false
console.log("isNumber('0.42a') => "+ isNumber('0.42a')); // false
console.log("isNumber('-4.2') => "+ isNumber('-4.2')); // true
console.log("isNumber('+4.2') => "+ isNumber('+4.2')); // true

console.log("isNumber('4e2') => "+ isNumber('4e2')); // true
console.log("isNumber('-4E2') => "+ isNumber('-4E2')); // true
console.log("isNumber('+4e-2') => "+ isNumber('+4e-2')); // true
console.log("isNumber('0.42E-.1234') => "+ isNumber('0.42E-.1234')); // true
console.log("isNumber('42e24e-123') => "+ isNumber('42e24e-123')); // false
console.log("isNumber('04.2E-.12.34') => "+ isNumber('04.2E-.12.34')); // false
console.log("isNumber('04.2E-.2134') => "+ isNumber('0.42E-.1234')); // true