Class: KPeg::Parser

Inherits:
StringScanner
  • Object
show all
Defined in:
lib/vendor/kpeg/lib/kpeg.rb

Defined Under Namespace

Classes: LeftRecursive, MemoEntry

Instance Attribute Summary (collapse)

Instance Method Summary (collapse)

Constructor Details

- (Parser) initialize(str, grammar)

A new instance of Parser



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 7

def initialize(str, grammar)
  super str

  @grammar = grammar
  # A 2 level hash.
  @memoizations = Hash.new { |h,k| h[k] = {} }

  @failing_pos = nil
  @failing_rule = nil
end

Instance Attribute Details

- (Object) failing_rule

Returns the value of attribute failing_rule



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 19

def failing_rule
  @failing_rule
end

- (Object) grammar (readonly)

Returns the value of attribute grammar



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 18

def grammar
  @grammar
end

- (Object) memoizations (readonly)

Returns the value of attribute memoizations



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 18

def memoizations
  @memoizations
end

Instance Method Details

- (Object) apply(rule) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 120

def apply(rule)
  if m = @memoizations[rule][pos]
    m.inc!

    self.pos = m.pos
    if m.ans.kind_of? LeftRecursive
      m.ans.detected = true
      return nil
    end

    return m.ans
  else
    lr = LeftRecursive.new(false)
    m = MemoEntry.new(lr, pos)
    @memoizations[rule][pos] = m
    start_pos = pos

    ans = rule.match(self)

    m.move! ans, pos

    # Don't bother trying to grow the left recursion
    # if it's failing straight away (thus there is no seed)
    if ans and lr.detected
      return grow_lr(rule, start_pos, m)
    else
      return ans
    end

    return ans
  end
end

- (Object) current_column(target = pos) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 37

def current_column(target=pos)
  offset = 0
  string.each_line do |line|
    len = line.size
    return (target - offset) if offset + len >= target
    offset += len
  end

  -1
end

- (Object) current_line(target = pos) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 48

def current_line(target=pos)
  cur_offset = 0
  cur_line = 0

  string.each_line do |line|
    cur_line += 1
    cur_offset += line.size
    return cur_line if cur_offset >= target
  end

  -1
end

- (Object) error_expectation 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 67

def error_expectation
  return "" unless @failing_rule

  error_pos = @failing_pos
  line_no = current_line(error_pos)
  col_no = current_column(error_pos)

  return "Expected #{@failing_rule.string.inspect} at line #{line_no}, column #{col_no} (offset #{error_pos})"
end

- (Object) fail(rule) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 31

def fail(rule)
  @failing_pos = pos
  @failing_rule = rule
  return nil
end

- (Boolean) failed?

Returns:

  • (Boolean) 


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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 168

def failed?
  !!@failing_rule
end

- (Object) grow_lr(rule, start_pos, m) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 153

def grow_lr(rule, start_pos, m)
  while true
    self.pos = start_pos
    ans = rule.match(self)
    return nil unless ans

    break if pos <= m.pos

    m.move! ans, pos
  end

  self.pos = m.pos
  return m.ans
end

- (Object) lines 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 61

def lines
  lines = []
  string.each_line { |l| lines << l }
  lines
end

- (Object) parse(name = nil) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 172

def parse(name=nil)
  if name
    rule = @grammar.find(name)
    unless rule
      raise "Unknown rule - #{name}"
    end

    match = apply rule
  else
    match = apply @grammar.root
  end

  if pos == string.size
    @failing_rule = nil
  end

  return match
end

- (Object) show_error(io = STDOUT) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 77

def show_error(io=STDOUT)
  return unless @failing_rule

  error_pos = @failing_pos
  line_no = current_line(error_pos)
  col_no = current_column(error_pos)

  io.puts "Expected #{@failing_rule.string.inspect} at line #{line_no}, column #{col_no} (offset #{error_pos})"
  io.puts "Got: #{string[error_pos,1].inspect}"
  io.puts "Rule: #{@failing_rule.inspect}"
  line = lines[line_no-1]
  io.puts "=> #{line}"
  io.print(" " * (col_no + 3))
  io.puts "^"
end

- (Object) switch_grammar(gram) 



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# File 'lib/vendor/kpeg/lib/kpeg.rb', line 21

def switch_grammar(gram)
  begin
    old = @grammar
    @grammar = gram
    yield
  ensure
    @grammar = old
  end
end