waeg.treetop

grammar Wae

  rule waestart
    statement:wae ';' {
    def eval
      statement.eval
    end
  }
  end
  
  rule wae
    terminal / expression
  end

  rule terminal 
    exit / id / num 
  end

  rule expression
    with /  sum / negop 
    {
      def eval
        expression.eval
      end
    }
  end
  
  rule with
    # {with {<id> <WAE>} <WAE>}
    '{' space operator_1:set space '{' space statement_1:assign space '}' space operand_3:wae space '}' {
      def eval(env={})
        operand_3.eval(env={statement_1.name => statement_1.val})
      end
    }
  end

  rule set
    'with'
  end

  rule assign
    operand_1:id space operand_2:wae {
      def eval(env)
        env[operand_1.name] = operand_2.eval(env)
      end
      def val
        operand_2.eval(env={})
      end
      def name
        operand_1.name
      end
    }
  end

  rule sum
    # {+ <WAE> <WAE>} | {- <WAE> <WAE>}
    '{' space operator_1:sum_op space operand_1:wae space operand_2:wae   space '}' {
      def eval(env={})
        operator_1.apply(operand_1.eval(env), operand_2.eval(env))
      end
    }
  end

  rule sum_op
    '+' {
      def apply(a, b)
        a + b
      end
    }
    / '-' {
      def apply(a,b)
        a - b
      end
    }
  end
  
  rule space
    ' '*
  end

  rule negop
    '-' operand_1:wae {
      def eval(env={})
        -operand_1.eval(env)
      end
    }
  end

  rule id
    [a-z] {
      def eval(env)
        env[name]
      end

      def name
        text_value
      end

      def bind(value, env)
        env.merge(name => value)
      end
    }
  end

  rule num
    ([1-9] [0-9]* / '0') {
       def eval(env = {})
         text_value.to_i
       end
    }
  end

   rule exit
     'exit' {
       def eval(env = {})
         puts "Goodbye"
         exit
       end
     }
   end

end