gistfile1.txt

describe "Conditional matching" do
  it "should understand binary/unary operators correctly, given the predecate to decide" do
    subject = Lexr.that {
      ignores /\s+/ => :whitespace
      
      legal_place_for_binary_operator = lambda { |prev| [:addition, 
                                                         :subtraction, 
                                                         :multiplication, 
                                                         :division,
                                                         :left_parenthesis,
                                                         :start].include? prev.type }

      matches "+" => :addition, :unless => legal_place_for_binary_operator
      matches "-" => :subtraction, :unless => legal_place_for_binary_operator
      matches "*" => :multiplication, :unless => legal_place_for_binary_operator
      matches "/" => :division, :unless => legal_place_for_binary_operator
      
      matches "(" => :left_parenthesis
      matches ")" => :right_parenthesis
      
      matches /[-+]?[0-9]*\.?[0-9]+/ => :number, :convert_with => lambda { |v| Float(v) }
    }
    
    lexer = subject.new("-10*(-3--2)")
    lexer.next.should == Lexr::Token.number(-10)
    lexer.next.should == Lexr::Token.multiplication("*")
    
    lexer.next.should == Lexr::Token.left_parenthesis("(")
    lexer.next.should == Lexr::Token.number(-3)
    lexer.next.should == Lexr::Token.subtraction("-")
    lexer.next.should == Lexr::Token.number(-2)
    lexer.next.should == Lexr::Token.right_parenthesis(")")

    lexer.next.should == Lexr::Token.end
  end
end