ahem/lib/ahem/ast/unary.rb

class AST::Unary
  attr_reader :operation, :expr

  def initialize(operation, expr)
    @operation = operation
    @expr = expr
  end

  def ==(other)
    other.operation == @operation && other.expr == @expr
  end

  def execute(env)
    case @operation
    when AST::Operators::SUBTRACT
      0.0 - @expr.execute(env)
    when AST::Operators::NOT
      !@expr.execute(env)
    end
  end
end