parsec.js

/*
 *  Parser combinator lib
 */

function is_error(x) {
  return typeof x === 'string';
}

function parser(f) {
  f.then = function(n, fc) {
    let f = this;
    return parser(i => {
      let a = f(i);
      if (is_error(a)) return a;
      else {
        let b = n(a[1]);
        if (is_error(b)) return b;
        else return fc? [fc(a[0],b[0]), b[1]] : ["" + a[0] + b[0], b[1]];
      }
    });
  }.bind(f);
  
  f._then = function(n) {
    let f = this;
    return parser(i => {
      let a = f(i);
      if (is_error(a)) return a;
      else {
        let b = n(a[1]);
        if (is_error(b)) return b;
        else return [b[0], b[1]];
      }
    });
  }.bind(f);

  f.then_ = function(n) {
    let f = this;
    return parser(i => {
      let a = f(i);
      if (is_error(a)) return a;
      else {
        let b = n(a[1]);
        if (is_error(b)) return b;
        else return [a[0], b[1]];
      }
    });
  }.bind(f);

  f.or = function(n) {
    let f = this;
    return parser(i => {
      let a = f(i);
      if (!is_error(a)) return a;
      else return n(i);
    });
  }.bind(f);

  f.pmap = function(n) {
    let f = this;
    return parser(i => {
      let a = f(i);
      if (!is_error(a)) return [n(a[0]), a[1]];
      else return a;
    });
  }.bind(f);
  
  f.named = function(n) {
    let f = this;
    this.nom = n;
    return parser(i => {
      let a = f(i);
      if (!is_error(a)) return a;
      else return "Expected " + f.nom;
    });
  }.bind(f);

  f.many = function(fc, fi) {
    let f = this;
    return parser(i => {
      let acc = fi || '';
      while (true) {
        let a = f(i);
        if (is_error(a)) return [acc, i];
        else {
          if(!fc) acc += a[0];
          else acc = fc(acc, a[0]);
          i = a[1];
        }
      }
    });
  }.bind(f);

  f.many1 = function(fc,fi) {
    let f = this;
    return parser(i => {
      let a = f(i);
      if(is_error(a)) return a;
      let acc = fi ? fi(a[0]) : a[0];
      i = a[1];
      while (true) {
        let a = f(i);
        if (is_error(a)) return [acc, i];
        else {
          if(!fc) acc += a[0];
          else acc = fc(acc, a[0]);
          i = a[1];
        }
      }
    });
  }.bind(f);

  return f;
}

function pseq(ps) {
  return ps.reduce((a, p) => a.then(p));
}

function palt(ps) {
  return ps.reduce((a, p) => a.or(p));
}

function pchar(c) {
  return parser(i => {
    if (!i) return 'unexpected end of input';
    else if (c === i[0]) return [c, i.slice(1)];
    else return "expected '" + c + "' but '" + i[0] + "' found";
  });
}

function pstr(c) {
  return pseq(c.split('').map(pchar)).named("'"+c+"'");
}

function ptok(t) {
  return parser(i => {
    if(!i) return 'unexpected end of input';
    else if (t === i[0].tok) return [i[0], i.slice(1)];
    else return "expected token " + t + " but " + i[0] + " found";
  });
}

function prange(a, b) {
  return parser(i => {
    if (!i) return 'unexpected end of input';
    else if (b >= i[0] && a <= i[0]) return [i[0], i.slice(1)];
    else return "expected '" + a + "'..'" + b + "' but '" + i[0] + "' found";
  });
}

function delimited(p, d) {
  return p.pmap(v => [v])
          .then(d._then(p, (a,b) => [a,b])
                 .many((acc,v) => acc.concat(v), []),
                (a,b) => a.concat(b));
} 

function delimitedAll(p, d) {
  return p.pmap(v => [v])
          .then(d.then(p, (a,b) => [a,b])
                 .many((acc,v) => acc.concat(v), []),
                (a,b) => a.concat(b));
} 

function dynamic(id) {
  return parser(i => global[id](i));
}

module.exports = { ptok, delimited, delimitedAll, palt, dynamic, parser };