Scala DSL - Simple Math

Question

I'm relatively new at Scala and I'm struggling with DSLs. Currently I'm trying to implement a simple Math DSL which could be used with some kind of natural language.

My Idea:

print(Calculate 4 plus 6)=> returns 10

print(Calculate 4 mins 2)=> returns 2 ... and so on

So far I have implemented two classes. The main class which serves just for calling the method and a calculation class. My Problem is a have no Idea how I could pass the first number to the calculation object, because It is not allowed to define parameters.

Could Anyone Help with an example or something?

Answer 1

You are going to run into some troubles making this feel like a natural language since the natural form that Scala wants to parse is class-instance method argument method argument method argument ..., which is rather unlike English.

However, here is a framework to get you started, with lots of extra boilerplate syntax to make the parsing work out right.

object Now {
  class Value(val please: Double) {
    def plus(d: Double) = new Value(please + d)
    def minus(d: Double) = new Value(please - d)
    override def toString = please.toString
  }
  def calculate(d: Double): Value = new Value(d)
}

And here it is working (after an import language.postfixOps):

scala> Now calculate 4 plus 6 please
res1: Double = 10.0

Incidentally, there's already a very good natural way to ask for 4+6...it's 4+6. It works for speakers of many different languages, and for almost all computer languages too. So this DSL might be fun for a toy, but I'm not sure what the practical utility is.