Class: Arithmetic::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/arithmetic/parser.rb

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(exp) ⇒ Parser

Returns a new instance of Parser.



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# File 'lib/arithmetic/parser.rb', line 8

def initialize(exp)
  @expression = exp
  @node_stack = []
end

Class Method Details

.is_a_number?(str) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/arithmetic/parser.rb', line 4

def self.is_a_number?(str)
  str.respond_to?(:to_str) && !!str.to_str.match(/^[\d\.]+$/)
end

Instance Method Details

#parse ⇒ Object

Raises:



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# File 'lib/arithmetic/parser.rb', line 13

def parse
  tokens = Tokenizer.new.tokenize(@expression)
  op_stack = []
 
  tokens.each do |token|
    if token.is_a? Operator
      # clear stack of higher priority operators
      while (!op_stack.empty? &&
             op_stack.last != "(" &&
             op_stack.last.priority >= token.priority)
        push_operator(op_stack.pop)
      end
 
      op_stack.push(token)
    elsif token == "("
      op_stack.push(token)
    elsif token == ")"
      while op_stack.last != "("
        push_operator(op_stack.pop)
      end
 
      # throw away the '('
      op_stack.pop
    else
      push_operand(token)
    end
  end
 
  until op_stack.empty?
    push_operator(op_stack.pop)
  end
 
  parsed_expression = @node_stack.pop
  raise InvalidExpression.new(@expression) unless @node_stack.empty?
  parsed_expression
end