I've finally took some time off this weekend to implement a simple object pattern matching facility as part of the newly created boo-extensions project.

Here's some code using the new 'match' and 'data' macros to implement an expression evaluator:

import Boo.PatternMatching
import Boo.Adt

def eval(e as Expression) as int:
   match e:
      case Const(value):
        return value
      case Add(left, right):
        return eval(left) + eval(right)

def simplify(e as Expression) as Expression:
    match e:
        case Add(left: Const(value: 0), right):
            return simplify(right)
        case Add(left, right: Const(value: 0)):
            return simplify(left)
        case Add(left, right):
            return Add(simplify(left), simplify(right))
        case _:
            return _

data Expression = Const(value as int) | Add(left as Expression, right as Expression)

e = Add(Add(Const(19), Const(0)), Add(Const(0), Const(23)))

print simplify(e)
print eval(e)
print eval(simplify(e))

'match' coupled with our recently acquired quasiquoting capabilities makes writing macros for boo a pleasant endeavour actually.

Dont believe me? Take a look at the data macro again.