;;;"alist.scm", alist functions for Scheme.
;;;Copyright (c) 1992, 1993 Aubrey Jaffer
;
;Permission to copy this software, to redistribute it, and to use it
;for any purpose is granted, subject to the following restrictions and
;understandings.
;
;1.  Any copy made of this software must include this copyright notice
;in full.
;
;2.  I have made no warrantee or representation that the operation of
;this software will be error-free, and I am under no obligation to
;provide any services, by way of maintenance, update, or otherwise.
;
;3.  In conjunction with products arising from the use of this
;material, there shall be no use of my name in any advertising,
;promotional, or sales literature without prior written consent in
;each case.

(define (predicate->asso pred)
  (cond ((eq? eq? pred) assq)
	((eq? = pred) assv)
	((eq? eqv? pred) assv)
	((eq? char=? pred) assv)
	((eq? equal? pred) assoc)
	((eq? string=? pred) assoc)
	(else (lambda (key alist)
		(let l ((al alist))
		  (cond ((null? al) #f)
			((pred key (caar al)) (car al))
			(else (l (cdr al)))))))))

(define (alist-inquirer pred)
  (let ((assofun (predicate->asso pred)))
    (lambda (alist key)
      (let ((pair (assofun key alist)))
	(and pair (cdr pair))))))

(define (alist-associator pred)
  (let ((assofun (predicate->asso pred)))
    (lambda (alist key val)
      (let* ((pair (assofun key alist)))
	(cond (pair (set-cdr! pair val)
		    alist)
	      (else (cons (cons key val) alist)))))))

(define (alist-remover pred)
  (lambda (alist key)
    (cond ((null? alist) alist)
	  ((pred key (caar alist)) (cdr alist))
	  ((null? (cdr alist)) alist)
	  ((pred key (caadr alist))
	   (set-cdr! alist (cddr alist)) alist)
	  (else
	   (let l ((al (cdr alist)))
	     (cond ((null? (cdr al)) alist)
		   ((pred key (caadr al))
		    (set-cdr! al (cddr al)) alist)
		   (else (l (cdr al)))))))))

(define (alist-map proc alist)
  (map (lambda (pair) (cons (car pair) (proc (car pair) (cdr pair))))
       alist))

(define (alist-for-each proc alist)
  (for-each (lambda (pair) (proc (car pair) (cdr pair))) alist))