How to write a simple macro in MIT Scheme?

Question

I am trying to translate this simple Common Lisp macro code to MIT Scheme code:

(defmacro calc (a op b)
  (list op a b))

(calc 2 + 3)

The above code prints 5 as expected.

How do I do the same thing in MIT scheme? Here is my attempt:

(defmacro (calc a op b)
  (list op a b))

(calc 2 + 3)

The above code fails with this error:

Unbound variable: b

What is the right way to write this code in MIT Scheme?

Answer 1

While many Scheme implementations has defmacro it differs if it has arguments like in Common Lisp, Scheme or if the expression is also a special form. It is not portable. From R5RS you can use `syntax-rules:

(define-syntax calc
  (syntax-rules () 
   ((_ a op b)   ; pattern  
    (op a b))))  ; expansion

(calc 4 + 3) ; ==> 7