# token-stream

Take an array of token and produce a more useful API to give to a parser.

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## Installation

    npm install token-stream

## Usage

```js
var TokenStream = require('token-stream');

var stream = new TokenStream([
  'a',
  'b',
  'c',
  'd'
]);
assert(stream.peek() === 'a');
assert(stream.lookahead(0) == 'a');
assert(stream.lookahead(1) == 'b');

assert(stream.advance() === 'a');
assert(stream.peek() === 'b');
assert(stream.lookahead(0) == 'b');
assert(stream.lookahead(1) == 'c');

stream.defer('z');
assert(stream.peek() === 'z');
assert(stream.lookahead(0) == 'z');
assert(stream.lookahead(1) == 'b');
assert(stream.advance() === 'z');
assert(stream.advance() === 'b');
assert(stream.advance() === 'c');
assert(stream.advance() === 'd');

// an error is thrown if you try and advance beyond the end of the stream
assert.throws(function () {
  stream.adavance();
});
```

## API

### stream.peek()

Gets and returns the next item in the stream without advancing the stream's position.

### stream.advance()

Returns the next item in the stream and advances the stream by one item.

### stream.defer(token)

Put a token on the start of the stream (useful if you need to back track after calling advance.

### stream.lookahead(index)

Return the item at `index` position from the start of the stream, but don't advance the stream.  `stream.lookahead(0)` is equivalent to `stream.peek()`.

## License

  MIT