Merge pull request #154 from /issues/150

Fixes #150; adds notFollowedBy

API.md

@@ -85,6 +85,10 @@ Like `Parsimmon.regexp(regexp)`, but yields only the text in the specific regexp
 
 This is an alias for `Parsimmon.regexp`.
 
+## Parsimmon.notFollowedBy(parser)
+
+Parses using `parser`, but does not consume what it parses. Yields an empty string if the parser *does not match* the input. Otherwise it fails.
+
 ## Parsimmon.lookahead(parser)
 
 Parses using `parser`, but does not consume what it parses. Yields an empty string.
@@ -482,6 +486,10 @@ var parserA = p1.skip(p2); // is equivalent to...
 var parserB = Parsimmon.seqMap(p1, p2, function(x1, x2) { return x1; });
 ```
 
+## parser.notFollowedBy(anotherParser)
+
+Returns a parser that looks for anything but whatever `anotherParser` wants to parse, and does not consume it. Yields the same result as `parser`. Equivalent to `parser.skip(Parsimmon.notFollowedBy(anotherParser))`.
+
 ## parser.lookahead(anotherParser)
 
 Returns a parser that looks for whatever `anotherParser` wants to parse, but does not consume it. Yields the same result as `parser`. Equivalent to `parser.skip(Parsimmon.lookahead(anotherParser))`.

CHANGELOG.md

@@ -1,3 +1,8 @@
+## version 1.3.0 (2017-??-??)
+
+* Adds `Parsimmon.notFollowedBy(parser)`
+* Adds `parser.notFollowedBy(anotherParser)`
+
 ## version 1.2.0 (2016-12-22)
 
 * Adds `Parsimmon.lookahead(parser)`

src/parsimmon.js

@@ -428,6 +428,11 @@
  _.lookahead = function(x) {
  return this.skip(lookahead(x));
  };
+
+ _.notFollowedBy = function(x) {
+ return this.skip(notFollowedBy(x));
+ };
+
  _.desc = function(expected) {
  var self = this;
  return Parsimmon(function(input, i) {
@@ -517,6 +522,17 @@
  throw new Error('not a string, regexp, or parser: ' + x);
  }
 
+ function notFollowedBy(parser) {
+ assertParser(parser);
+ return Parsimmon(function(input, i) {
+ var result = parser._(input, i);
+ var text = input.slice(i, result.index);
+ return result.status
+ ? makeFailure(i, 'not "' + text + '"')
+ : makeSuccess(i, null);
+ });
+ }
+
  var any = Parsimmon(function(input, i) {
  if (i >= input.length) {
  return makeFailure(i, 'any character');
@@ -666,6 +682,7 @@
  Parsimmon.letter = letter;
  Parsimmon.letters = letters;
  Parsimmon.lookahead = lookahead;
+ Parsimmon.notFollowedBy = notFollowedBy;
  Parsimmon.makeFailure = makeFailure;
  Parsimmon.makeSuccess = makeSuccess;
  Parsimmon.noneOf = noneOf;

test/parsimmon.test.js

@@ -15,6 +15,7 @@ suite('parser', function() {
  var lazy = Parsimmon.lazy;
  var fail = Parsimmon.fail;
  var lookahead = Parsimmon.lookahead;
+ var notFollowedBy = Parsimmon.notFollowedBy;
 
  function equivalentParsers(p1, p2, inputs) {
  for (var i = 0; i < inputs.length; i++) {
@@ -121,6 +122,37 @@ suite('parser', function() {
  assert.deepEqual(answer, expectation);
  });
 
+ suite('Parsimmon.notFollowedBy', function() {
+ test('fails when its parser argument matches', function() {
+ var weirdParser = string('dx');
+ var parser = seq(
+ string('abc'),
+ notFollowedBy(weirdParser).result('NOT USED'),
+ string('dx')
+ );
+ var answer = parser.parse('abcdx');
+ assert.deepEqual(answer.expected, ['not "dx"']);
+ });
+ test('does not consume from its input', function() {
+ var weirdParser = string('Q');
+ var parser = seq(
+ string('abc'),
+ notFollowedBy(weirdParser),
+ string('d')
+ );
+ var answer = parser.parse('abcd');
+ assert.deepEqual(answer.value, ['abc', null, 'd']);
+ });
+ test('can be chained from prototype', function() {
+ var parser = seq(
+ string('abc').notFollowedBy(string('Q')),
+ string('d')
+ );
+ var answer = parser.parse('abcd');
+ assert.deepEqual(answer.value, ['abc', 'd']);
+ });
+ });
+
  suite('Parsimmon.lookahead', function() {
  test('should handle a string', function() {
  lookahead('');
@@ -225,7 +257,7 @@ suite('parser', function() {
  var parser =
  seq(
  string('('),
- regex(/[^\)]/).many().map(function(xs) {
+ regex(/[^)]/).many().map(function(xs) {
  return xs.join('');
  }),
  string(')')
@@ -245,7 +277,7 @@ suite('parser', function() {
  line: 1,
  column: 8
  },
- expected: ['\')\'', '/[^\\)]/']
+ expected: ['\')\'', '/[^)]/']
  }
  );