common-macros.scm

;;;
;;; common-macros.scm - common macros
;;;
;;;   Copyright (c) 2000-2024  Shiro Kawai  <shiro@acm.org>
;;;
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;; This file used to have a bunch of fundamental macro definitions.
;; Now most of them are compiled into the core (libmacro.scm).  We only keep
;; serveral less-used macros here.  They are autoloaded.

(define-module gauche.common-macros
  (export get-optional get-keyword* fluid-let while until))
(select-module gauche.common-macros)

;;;-------------------------------------------------------------
;;; bind construct

;; fluid-let written by Dorai Sitaram
;; NB: all threads shares the state of fluid global vers.
;; this is mainly for the comatibility of existing third-party code.
(define-macro fluid-let
  (lambda (varvals . body)
    (let ((vars (map car varvals))
          (vars-twins (map (lambda (ig) (gensym)) varvals))
          (swap (gensym))
          (temp (gensym)))
      `(let (,@(map list vars-twins (map cadr varvals)))
         (let ((,swap
                (lambda ()
                  ,@(map (lambda (var twin)
                           `(let ((,temp ,var))
                              (set! ,var ,twin)
                              (set! ,twin ,temp)))
                         vars vars-twins))))
           (dynamic-wind
               ,swap
               (lambda () ,@body)
               ,swap))))))

;;;-------------------------------------------------------------
;;; useful argument utility

(define-syntax get-keyword*
  (syntax-rules ()
    [(_ key lis default)
     (let ((li lis))
       (let loop ((l li))
         (cond ((null? l) default)
               ((null? (cdr l)) (error "keyword list not even" li))
               ((eq? key (car l)) (cadr l))
               (else (loop (cddr l))))))]
    [(_ key lis) (get-keyword key lis)]))

(define-syntax get-optional
  (syntax-rules ()
    [(_ args default)
     (let ((a args))
       (if (pair? a) (car a) default))]
    [(_ . other)
     (syntax-error "badly formed get-optional" (get-optional . other))]
    ))

;;;-------------------------------------------------------------
;;; repeat construct

(define-syntax while
  (syntax-rules (=>)
    [(_ expr guard => var . body)
     (do ((var expr expr))
         ((not (guard var)))
       . body)]
    [(_ expr => var . body)
     (do ((var expr expr))
         ((not var))
       . body)]
    [(_ expr . body)
     (do ()
         ((not expr))
       . body)]
    [(_ . other)
     (syntax-error "malformed while" (while . other))]))

(define-syntax until
  (syntax-rules (=>)
    [(_ expr guard => var . body)
     (do ((var expr expr))
         ((guard var))
       . body)]
    [(_ expr => var . body)
     (do ((var expr expr))
         (var)
       . body)]
    [(_ expr . body)
     (do ()
         (expr)
       . body)]
    [(_ . other)
     (syntax-error "malformed until" (until . other))]))