Class: Crass::Scanner

Inherits:
Object
  • Object
show all
Defined in:
lib/crass/scanner.rb

Overview

Similar to a StringScanner, but with extra functionality needed to tokenize CSS while preserving the original text.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(input) ⇒ Scanner

Creates a Scanner instance for the given input string or IO instance.



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# File 'lib/crass/scanner.rb', line 24

def initialize(input)
  @string = input.is_a?(IO) ? input.read : input.to_s
  @chars  = @string.chars.to_a

  reset
end

Instance Attribute Details

#current ⇒ Object (readonly)

Current character, or nil if the scanner hasn't yet consumed a character, or is at the end of the string.



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# File 'lib/crass/scanner.rb', line 10

def current
  @current
end

#marker ⇒ Object

Current marker position. Use #marked to get the substring between #marker and #pos.



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# File 'lib/crass/scanner.rb', line 14

def marker
  @marker
end

#pos ⇒ Object

Position of the next character that will be consumed. This is a character position, not a byte position, so it accounts for multi-byte characters.



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# File 'lib/crass/scanner.rb', line 18

def pos
  @pos
end

#string ⇒ Object (readonly)

The string being scanned.



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# File 'lib/crass/scanner.rb', line 21

def string
  @string
end

Instance Method Details

#consume ⇒ Object

Consumes the next character and returns it, advancing the pointer, or an empty string if the end of the string has been reached.



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# File 'lib/crass/scanner.rb', line 33

def consume
  @current = @chars[@pos] || ''
  @pos += 1 if @current
  @current
end

#consume_rest ⇒ Object

Consumes the rest of the string and returns it, advancing the pointer to the end of the string. Returns an empty string is the end of the string has already been reached.



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# File 'lib/crass/scanner.rb', line 42

def consume_rest
  rest     = @string[@pos..@len] || ''
  @current = rest[-1] || ''
  @pos     = @len

  rest
end

#eos? ⇒ Boolean

Returns true if the end of the string has been reached, false otherwise.

Returns:

  • (Boolean) 


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# File 'lib/crass/scanner.rb', line 52

def eos?
  @pos == @len
end

#mark ⇒ Object

Sets the marker to the position of the next character that will be consumed.



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# File 'lib/crass/scanner.rb', line 58

def mark
  @marker = @pos
end

#marked ⇒ Object

Returns the substring between #marker and #pos, without altering the pointer.



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# File 'lib/crass/scanner.rb', line 64

def marked
  if result = @chars[@marker...@pos]
    result.join('')
  else
    ''
  end
end

#peek(length = 1) ⇒ Object

Returns up to length characters starting at the current position, but doesn't consume them. The number of characters returned may be less than length if the end of the string is reached.



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# File 'lib/crass/scanner.rb', line 75

def peek(length = 1)
  if result = @chars[@pos, length]
    result.join('')
  else
    ''
  end
end

#reconsume ⇒ Object

Moves the pointer back one character without changing the value of #current. The next call to #consume will re-consume the current character.



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# File 'lib/crass/scanner.rb', line 86

def reconsume
  @pos -= 1 if @pos > 0
end

#reset ⇒ Object

Resets the pointer to the beginning of the string.



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# File 'lib/crass/scanner.rb', line 91

def reset
  @current = nil
  @len     = @string.length
  @marker  = 0
  @pos     = 0
end

#scan(pattern) ⇒ Object

Tries to match pattern at the current position. If it matches, the matched substring will be returned and the pointer will be advanced. Otherwise, nil will be returned.



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# File 'lib/crass/scanner.rb', line 101

def scan(pattern)
  match = pattern.match(@string, @pos)
  return nil if match.nil? || match.begin(0) != @pos

  @pos     = match.end(0)
  @current = @chars[@pos - 1]

  match[0]
end

#scan_until(pattern) ⇒ Object

Scans the string until the pattern is matched. Returns the substring up to and including the end of the match, and advances the pointer. If there is no match, nil is returned and the pointer is not advanced.



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# File 'lib/crass/scanner.rb', line 114

def scan_until(pattern)
  start = @pos
  match = pattern.match(@string, @pos)

  return nil if match.nil?

  @pos     = match.end(0)
  @current = @chars[@pos - 1]

  @string[start...@pos]
end