Class: ExpressionParser::Lexer

Inherits:
Object
  • Object
show all
Defined in:
lib/expression_parser/lexer.rb

Instance Method Summary collapse

Constructor Details

#initialize(input) ⇒ Lexer

Returns a new instance of Lexer.



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# File 'lib/expression_parser/lexer.rb', line 6

def initialize(input)
  @input = input
  @return_previous_token = false
end

Instance Method Details

#get_next_token ⇒ Object 



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# File 'lib/expression_parser/lexer.rb', line 11

def get_next_token
  if @return_previous_token
	@return_previous_token = false
	return @previous_token
  end

  token = Token.new

  @input.lstrip!

  case @input
  when /\A\+/ then
	token.kind = Token::Plus
  when /\A-/ then
	token.kind = Token::Minus
  when /\A\*/ then
	token.kind = Token::Multiply
  when /\Adiv/ then
	token.kind = Token::Divide
  when /\A\// then
	token.kind = Token::Divide
  when /\A\d+(\.\d+)?/
	token.kind = Token::Number
	token.value = $&.to_f
  when /\A\(/
	token.kind = Token::LParen
  when /\A\)/
	token.kind = Token::RParen
  when ''
	token.kind = Token::End
  when /\Ae/
	token.kind = Token::Number
	token.value = 2.718281828459
  when /\Api/
	token.kind = Token::Number
	token.value = 3.1415926535898
  when /\Amod/
	token.kind = Token::MOD
  when /\A!=/
	token.kind = Token::NotEqual
  when /\A<>/
	token.kind = Token::NotEqual
  when /\A>=/
	token.kind = Token::GThanE
  when /\A>/
	token.kind = Token::GThan
  when /\A<=/
	token.kind = Token::LThanE
  when /\A</
	token.kind = Token::LThan
  when /\A=/
	token.kind = Token::Equal
  end

  raise "Unknown token #{@input}" if token.unknown?
  @input = $'

  @previous_token = token
  token
end

#revert ⇒ Object 



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# File 'lib/expression_parser/lexer.rb', line 72

def revert
  @return_previous_token = true
end