class ParseQueue

The RCTP queue for parser token flow with backtracking.

Constants

DFB: The default fetch block
VERSION

Attributes

position[R]

The current read point of the queue.

Public Class Methods

new(&fetch) click to toggle source

Set up the parser queue.

# File lib/parse_queue.rb, line 17
def initialize(&fetch)
  @fetch  = fetch
  @buffer = []
  @offset = @position = 0
end

Public Instance Methods

fetch_all() click to toggle source

Fetch all possible items.

# File lib/parse_queue.rb, line 50
def fetch_all
  loop do
    item = @fetch.call

    unless item
      @fetch = DFB
      return
    end

    @buffer << item
  end
end

fwd_count() click to toggle source

How many unread items are in this parse queue?

# File lib/parse_queue.rb, line 24
def fwd_count
  index_limit - @position
end

get() click to toggle source

Get an item from the buffer.

# File lib/parse_queue.rb, line 34
def get
  @buffer << fetch_one if @position == index_limit

  result = @buffer[rev_count]
  @position += 1
  result
end

get!() click to toggle source

Get an item and shift the buffer.

# File lib/parse_queue.rb, line 43
def get!
  result = get
  shift
  result
end

position=(value) click to toggle source

Set the position

# File lib/parse_queue.rb, line 64
def position=(value)
  @position = value
  validate_position
end

rev_count() click to toggle source

How many already read items are still in this parse queue?

# File lib/parse_queue.rb, line 29
def rev_count
  @position - @offset
end

shift() click to toggle source

Release any items before the current item.

# File lib/parse_queue.rb, line 76
def shift
  @buffer.shift(rev_count)
  @offset = @position
end

try(&block) click to toggle source

Try to process some items with roll back on failure.

# File lib/parse_queue.rb, line 82
def try(&block)
  save = @position
  self.position = save unless (result = block.call)
  result
end

try!(&block) click to toggle source

Process some items with a shift on success and a roll back on failure.

# File lib/parse_queue.rb, line 89
def try!(&block)
  shift if (result = try(&block))
  result
end

unget(count=1) click to toggle source

Undo the last get.

# File lib/parse_queue.rb, line 70
def unget(count=1)
  @position -= count
  validate_position
end

Private Instance Methods

fetch_one() click to toggle source

Fetch a single item.

# File lib/parse_queue.rb, line 108
def fetch_one
  item = @fetch.call

  unless item
    @fetch = DFB
    fail ParseQueueNoFwd
  end

  item
end

index_limit() click to toggle source

The first index past the end of the array

# File lib/parse_queue.rb, line 103
def index_limit
  @buffer.length + @offset
end

validate_position() click to toggle source

Is this a valid position?

# File lib/parse_queue.rb, line 97
def validate_position
  fail ParseQueueNoRev if @position < @offset
  fail ParseQueueNoFwd if @position >= index_limit
end