Parsing API

parser.js

// It would be this:
//---
var Literal = clone(Base, {
  // :: Str → Literal
  make: function make(text) {
    return clone(Literal, { text: String(text) })
  },

  // :this: ParserState → [Token, ParserState]
  parse: function parse(ps) {
    var text = this.text
    return ps.match(text)?  [Token.copy('LITERAL', text), ps.move(text.length)]
         : /* failed? */    [null, ps]
  },

  // :this: ParserState → Error
  failed: function failed(ps) {
    return new SyntaxError( this.error(ps)
                          + '\n Arising from ' + ps.describe()
                          + '\n\n'
                          + ps.snippet())
  },

  // :this: ParserState → Str
  error: function error(ps) {
    return 'Expected the literal "' + this.text + '", '
         + 'got "' + ps.lookahead(this.text.length) + '" instead.'
  }
})
//---

// Instead of this:
//---
function literal(text) { return function(ps) {
  return ps.match(text)?  [Token.copy('LITERAL', text), ps.move(text.length)]
       : /* failed? */    [null, ps]
}}
//---


// That is, given the error handling is performed by operators, like the
// `required' one:
function required(matcher){ return function(ps) { var result
  result = matcher.parse(ps)
  if (failedp(result))  throw matcher.failed(ps)

  return result
}}