[Jscheme-user] learning from other languages.

[Ken A. <kan...@bb...>]

Geoffrey reminded me that its good to take inspiration from other
languages.  Here are some macros i've been playing with.


;;; Alternatives to lambda.
(define-macro (\\ args . body) `(lambda ,args ,@body))

;; Convenient for writing simple one argument functions.
(define-macro (_ . body) `(lambda (_) ,@body))

(define-macro (| . body)
  ;; Ruby like: (| a b | (* a (+ 1 b))) -> (lambda (a b) (* a (+ 1 b)))
  (define (crack rest sofar)
    (cond ((null? rest) (error "No closing | found!"))
	  ((eq? (car rest) '|) (cons (reverse sofar) (cdr rest)))
	  (else (crack (cdr rest) (cons (car rest) sofar)))))
  (mvbind (args . body) (crack body '())
	  `(lambda ,args ,@body)))

(define-macro (mvbind pattern source . body)
  ;; Like multiple-value-bind.
  `(apply (lambda ,pattern ,@body) ,source))

(define-macro (while cond . actions)
  `(let loop ()
     (if ,cond (begin ,@(append actions (list '(loop)))))))

(define-macro (for var vals . body)
  ;; Python like for loop
  ;; Example: (for x in xs if (prime? x) (print x))
  (if (eq? (car body) 'if) `(for-each* (lambda (,var) ,body) ,vals)
      `(for-each* (lambda (,var) ,@body) ,vals)))

(define-macro (lt var val . body)
  ;; Arc 1 variable let.
  `(let ((,var ,val))
     ,@body))

(define-macro (if. . args)
  ;; Arc if.
  (if (null? args) '()
      (if (null? (cdr args))
          (car args)
          `(if ,(car args) ,(cadr args)
               (if. ,@(cddr args))))))