Class: ShuntingYard

Inherits:
Object
  • Object
show all
Defined in:
lib/lamep/shunting_yard.rb

Instance Method Summary collapse

Constructor Details

#initialize(tokens) ⇒ ShuntingYard

Returns a new instance of ShuntingYard.



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# File 'lib/lamep/shunting_yard.rb', line 3

def initialize(tokens)
  fail ArgumentError.new("Expected array: Got #{tokens.class}") unless tokens.is_a?(Array)
  @tokens = tokens
end

Instance Method Details

#burn_stack_to_higher_precedence(token) ⇒ Object 



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# File 'lib/lamep/shunting_yard.rb', line 35

def burn_stack_to_higher_precedence(token)
  until @stack.empty? || @stack.last == '(' || Operator.precedence!(token) < Operator.precedence!(@stack.last)
    @output << @stack.pop
  end
end

#postfix ⇒ Object 



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# File 'lib/lamep/shunting_yard.rb', line 8

def postfix
  @output = []
  @stack = []
  bracket_sum = 0
  @tokens.each do |token|
    case token
      when '('
        bracket_sum += 1
        @stack << token
      when ')'
        bracket_sum -= 1
        fail('Right parentheses mismatch') if bracket_sum < 0
        burn_stack_to_parentheses
      else
        if Operator.exists?(token)
          burn_stack_to_higher_precedence(token)
          @stack << token
        else
          @output << token
        end
    end
  end
  fail('Left parentheses mismatch') if bracket_sum > 0
  @output += @stack.reverse
  @output
end