Schemin

Schemin is a BSD-licensed scheme-ish interpreter, written in C#. Schemin is complete enough to run some simple scheme snippets, such as this example bubblesort routine:

(define bubblesort (lambda (l)
  (define swap-pass (lambda (l)
    (if (eq? (length l) 1) 
        l
        (let ((fst (car l))(snd (cadr l))(rest (cddr l)))
          (if (> fst snd) 
              (cons snd (swap-pass (cons fst rest)))
              (cons fst (swap-pass (cons snd rest))))))))
  (let for ((times (length l)) (val l))
    (if (> times 1)
        (for (- times 1)(swap-pass val))
        (swap-pass val)))))

As well as some more complicated things, like this simple example of coroutines using call/cc:

(define (superfluous-computation do-other-stuff) 
  (let loop () 
    (map (lambda (graphic) 
      (display graphic) 
      (newline) 
      (set! do-other-stuff (call/cc do-other-stuff))) 
    '("Straight up." "Quarter after." "Half past."  "Quarter til.")) 
  (loop))) 

(define (hefty-computation do-other-stuff) 
 (let loop ((n 5)) 
  (display "Hefty computation: ") 
  (display n) 
  (newline) 
  (set! do-other-stuff (call/cc do-other-stuff)) 
  (display "Hefty computation (b)")  
  (newline) 
  (set! do-other-stuff (call/cc do-other-stuff)) 
  (display "Hefty computation (c)") 
  (newline) 
  (set! do-other-stuff (call/cc do-other-stuff)) 
  (if (> n 0) 
   (loop (- n 1))))) 

(hefty-computation superfluous-computation)

Or this basic macro, which adds the arguments given to it, using a quasiquoting template:

(define-macro (testadd . toadd) `(fold (lambda (acc x) (+ acc x)) 0 (list ,@toadd)))

Check out the examples directory for more examples of what Schemin is capable of.

Implemented featues:

• Basic unhygenic macros, using define-macro paired with quasiquoting.
• All primitive types in r5rs, except the full numerical tower.
• First-class continuations and call/cc
• IO Ports (File and console IO)
• define and set!
• lambdas with closures
• Let, named let, Let*, and letrec
• Some flow control (if, cond, and, or and boolean primitives)
• A few list operations like map, filter, and foldl (as well as cons, cdr, car, etc)
• Some basic numerical primitives and decimal support

To do:

• Possibly implement a parser generator instead of our recursive parser
• Implement more common primitives
• Implement hygenic macros