Title

Handling rest list

Author

Joo ChurlSoo

Related SRFIs

The procedure and macros proposed in this SRFI make a strong combination with
RECEIVE (SRFI 8) and LET-VALUES (SRFI 11).

Abstract

This SRFI introduces the REST-VALUES procedure which has three modes of
operation:

1. it processes a rest list after checking its elements with default values or
   predicate procedures,

2. it processes a rest list with default values without checking its elements;
   the ARG-AND, ARG-ANDS, ERR-AND, and ERR-ANDS macros check the rest
   arguments that are returned by REST-VAULES that functions as the latter.

3. it processes a default list whose elements are lists or pairs, after
   checking their elements that are default values or predicate procedures
   with the elements of a rest list.

Rationale

When defining a procedure with a variable number of arguments, REST-VALUES
with or without ARG-AND (or ARG-ANDS or ERR-AND or ERR-ANDS) reduces the
clutter of various conditionals and error conditions.

Specification

(REST-VALUES [<caller>] <rest-list> [<args-number-limit> <default> ...])

    * <caller> is any scheme expression.
    * <args-number-limit> should be an integer, +, -, or a boolean.

    * 1. When the <args-number-limit> is + or a positive integer,
    	 each <default> should be a list that contains default value(s), or a
	 pair whose car is a default value and whose cdr is a predicate
	 procedure.
      2. When the <args-number-limit> is - or a negative integer,
	 each <default> is any scheme expression. 
      3. When the <args-number-limit> is a boolean,
	 each <default> is the same as 1.

1. (first mode of operation)
   REST-VALUES checks whether each element of the <rest-list> is a member of
   the corresponding <default> list, or satisfies the predicate procedure of
   the corresponding <default> pair, and then returns the checked element(s).
   If the element doesn't pass, REST-VALUES signals an error.  When there are
   no more elements in the <rest-list>, then REST-VALUES additionally returns
   the car values of the remaining <default>s.  On the other hand, when the
   number of elements of the <rest-list> are more than the number of the
   <default>s, the supernumerary elements are additionally returned if the
   <args-number-limit> is +, or its value is not less than the number of
   elements of the <rest-list>.

2. (second mode of operation)
   This is the same as the first except that REST-VALUES does not check each
   element of the <rest-list>, and it uses - instead of +, and an absolute
   value instead of a simple value as the value of <args-number-limit>.

3. (third mode of operation)

   REST-VALUES checks whether any element of the <default> list is a member of
   the <rest-list>, or any element of the <rest-list> satisfies the predicate
   procedure of the <default> pair, and then returns the checked element.  If
   the <default> doesn't pass, REST-VALUES returns the car value of the
   <default>.  When any elements of the <rest-list> are remained after the
   above processing, REST-VALUES either signals an error if the
   <args-number-limit> is #t, or return the remaining elements of the
   <rest-list> if the <args-number-limit> is #f.

(ARG-AND [<caller>] <variable> <expr> ...)
(ARG-ANDS [COMMON <caller>] ([<caller>] <variable> <expr> ...) ...)
(ERR-AND <caller> <expression> ...)
(ERR-ANDS (<caller> <expression> ...) ...)

(ARG-OR [<caller>] <variable> <expr> ...)
(ARG-ORS [COMMON <caller>] ([<caller>] <variable> <expr> ...) ...)
(ERR-OR <caller> <expression> ...)
(ERR-ORS (<caller> <expression> ...) ...)

    * Each <variable> should be an argument of a procedure.
    * The <caller>, <expr>, and <expression> are any scheme expressions, but
      the <expr> should contain the corresponding <variable>.

ARG-AND, ARG-ANDS, ERR-AND, and ERR-ANDS are the same as AND except that these
signal an error in case AND returns a false value.

ARG-OR, ARG-ORS, ERR-OR, and ERR-ORS are the same as OR except that these
signal an error in case OR returns a true value.

Examples

caller    => <procedure caller>
rest-list => (x 1)
(rest-values rest-list)	                 => x 1
(rest-values rest-list 2)	         => x 1
(rest-values caller rest-list)           => x 1
(rest-values caller rest-list -3)        => x 1
(rest-values rest-list -2 'y 3 "str")
    => error too many defaults (y 3 "str") (<= (length (y 3 "str")) 2)
(rest-values caller rest-list 1 '(x y z))
    => error too many arguments (x 1) (<= (length (x 1)) 1) <procedure caller>
(rest-values 'caller rest-list 2 (list 'x 'y 'z) (cons "str" string?))
    => error incorrect argument 1 (<procedure string?> 1) caller
(rest-values rest-list 2 '(y z) `(100 . ,number?))
    => error unmatched argument x (member x (y z))
(rest-values `(caller ,@rest-list) rest-list 2 '(y z) `(100 . ,number?))
    => error unmatched argument x (member x (y z)) (caller x 1)
(rest-values "caller: bad argument" rest-list 2 '(y z) `(100 . ,number?))
    => error caller: bad argument x (member x (y z))
(rest-values rest-list - 'y 100 "str")
    => x 1 "str"
(rest-values rest-list + `(x y z) `(100 . ,number?) `("str" . ,string?))
    => x 1 "str"
(rest-values rest-list #t `(x y z) `(100 . ,number?) `("str" . ,string?))
    => x 1 "str"
(rest-values rest-list #t `(100 . ,number?) `("str" . ,string?) `(x y z))
    => 1 "str" x
(rest-values rest-list #t `(100 . ,number?) `("str" . ,string?) `(y z))
    => error bad argument (x) (null? (x))
(rest-values rest-list #f `(100 . ,number?) `("str" . ,string?) `(y z))
    => 1 "str" y x

caller => <procedure caller>
str    => "string"
num    => 2
(arg-and num (number? num) (< num 2))
       => error incorrect argument 2 num (< num 2)
(arg-and caller num (number? num) (< num 2))
       => error incorrect argument 2 num (< num 2) <procedure caller>
(arg-and 'caller num (number? num) (< num 2))
       => error incorrect argument 2 num (< num 2) caller
(arg-and `(caller ,str ,num) num (number? num) (< num 2))
       => error incorrect argument 2 num (< num 2) (caller "string" 2)
(arg-and "caller: bad argument" num (number? num) (< num 2))
       => error caller: bad argument 2 num (< num 2)
(arg-ands (str (string? str) (< (string-length str) 7))
	  ("caller: bad argument" num (number? num) (< num 2)))
       => error caller: bad argument 2 num (< num 2)
(arg-ands ("caller: bad argument" str (string? str) (< (string-length str) 7))
	  (num (number? num) (< num 2)))
       => error incorrect argument 2 num (< num 2)
(arg-ands common 'caller
	  (str (string? str) (< (string-length str) 7))
	  (num (number? num) (< num 2)))
       => error incorrect argument 2 num (< num 2) caller
(arg-ands common `(caller ,str ,num)
	  (str (string? str) (< (string-length str) 7))
	  ('caller num (number? num) (< num 2)))
       => error incorrect argument 2 num (< num 2) caller
(arg-ands common "caller: bad argument"
	  (str (string? str) (< (string-length str) 7))
	  ("caller: incorrect argument" num (number? num) (< num 2)))
       => error caller: incorrect argument 2 num (< num 2)
(err-and 'caller
	 (string? str) (< (string-length str) 7) (number? num) (< num 2))
       => error false expression (< num 2) caller
(err-ands (caller (string? str) (< (string-length str) 7))
	  ("num failed test in caller" (number? num) (< num 2)))
       => error num failed test in caller (< num 2)

(define (read-line . p-d)
  ;; p-d should be (<input-port> <symbol>).
  (receive (p d) (rest-values p-d 2
			      (cons (current-input-port) input-port?)
			      (list 'trim 'concat 'split...))
    ...))
(define (read-line . p-d)
  (receive (p d) (rest-values p-d -2 (current-input-port) 'trim)
    (arg-ands (p (input-port? p))
	      (d (memq d '(trim concat split...))))
    ...))
(define (read-line . p-d)
  ;; p-d can be (<input-port> <symbol>) or (<symbol> <input-port>).
  (receive (p d) (rest-values p-d #t
			      (cons (current-input-port) input-port?)
			      (list 'trim 'concat 'split...))
    ...))

(define (delete x ls . predicate)
  (let ((pred (rest-values 'delete predicate 1 (list equal? eqv? eq?))))
    ...))
(define (delete x ls . predicate)
  (let ((pred (rest-values 'delete predicate -1 equal?)))
    (err-and 'delete (list? ls) (memq pred (list equal? eqv? eq?)))
    ...))

(define (substring str . start-end)
  (let ((str-len (arg-and substring str (string? str) (string-length str))))
    (receive (start end) (rest-values substring start-end -2 0 str-len)
      (arg-ands common substring
		(start (integer? start) (<= 0 start str-len))
		(end (integer? end) (<= start end str-len)))
      ...)))

Implementation

ERROR (SRFI 23) and TAKE (SRFI 1) are used in implementation of this SRFI.

(define (rest-values rest-list . default-list)
  (let* ((caller (if (or (null? default-list)
			 (boolean? (car default-list))
			 (memq (car default-list) (list + -))
			 (number? (car default-list)))
		     '()
		     (if (string? rest-list) rest-list (list rest-list))))
	 (rest (if (null? caller) rest-list (car default-list)))
	 (rest-length (if (list? rest)
			  (length rest)
			  (if (string? caller)
			      (error caller rest `(list? ,rest))
			      (apply error "bad rest list" rest `(list? ,rest)
				     caller))))
	 (default (if (null? caller) default-list (cdr default-list)))
	 (number
	  (and (not (null? default))
	       (let ((d (car default)))
		 (or (and (number? d)
			  (or (and (> rest-length (abs d))
				   (if (string? caller)
				       (error caller rest
					      `(<= (length ,rest) ,(abs d)))
				       (apply error "too many arguments" rest
					      `(<= (length ,rest) ,(abs d))
					      caller)))
			      (and (> (length (cdr default)) (abs d))
				   (if (string? caller)
				       (error caller (cdr default)
					      `(<= (length ,(cdr default))
						   ,(abs d)))
				       (apply error "too many defaults"
					      (cdr default)
					      `(<= (length ,(cdr default))
						   ,(abs d))
					      caller)))
			      d))
		     (and (eq? d +) +)
		     (and (eq? d -) -)
		     (and (eq? d #f) 'false)
		     (eq? d #t)
		     (if (string? caller)
			 (error caller d `(or (boolean? ,d)
					      (number? ,d)
					      (memq ,d (list + -))))
			 (apply error "bad optional argument" d
				`(or (boolean? ,d)
				     (number? ,d)
				     (memq ,d (list + -)))
				caller))))))
	 (default (if number (cdr default) default))
	 (default-length (length default)))
    (cond
     ((or (eq? 'false number) (eq? #t number))
      (let loop ((rest-list rest)
		 (default-list default)
		 (result '()))
	(if (null? default-list)
	    (if (eq? #t number)
		(if (null? rest-list)
		    (apply values (reverse result))
		    (if (string? caller)
			(error caller rest-list `(null? ,rest-list))
			(apply error "bad argument" rest-list
			       `(null? ,rest-list) caller)))
		(apply values (append (reverse result) rest-list)))
	    (let ((default (car default-list)))
	      (if (or (list? default)
		      (and (pair? default) (procedure? (cdr default))))
		  (let lp ((rest rest-list)
			   (head '()))
		    (if (null? rest)
			(loop (reverse head)
			      (cdr default-list)
			      (cons (car default) result))
			(if (list? default)
			    (if (member (car rest) default)
				(loop (append (reverse head) (cdr rest))
				      (cdr default-list)
				      (cons (car rest) result))
				(lp (cdr rest) (cons (car rest) head)))
			    (if ((cdr default) (car rest))
				(loop (append (reverse head) (cdr rest))
				      (cdr default-list)
				      (cons (car rest) result))
				(lp (cdr rest) (cons (car rest) head))))))
		  (if (string? caller)
		      (error caller default
			     `(or (list? ,default)
				  (and (pair? ,default)
				       (procedure? (cdr ,default)))))
		      (apply error "bad default" default
			     `(or (list? ,default)
				  (and (pair? ,default)
				       (procedure? (cdr ,default))))
			     caller)))))))
     ((or (and (number? number) (> number 0))
	  (eq? number +))
      (let ((number (min rest-length default-length)))
	(for-each (lambda (r d)
		    (cond
		     ((list? d)
		      (if (not (member r d))
			  (if (string? caller)
			      (error caller r `(member ,r ,d))
			      (apply error "unmatched argument"
				     r `(member ,r ,d) caller))))
		     ((and (pair? d) (procedure? (cdr d)))
		      (if (not ((cdr d) r))
			  (if (string? caller)
			      (error caller r `(,(cdr d) ,r))
			      (apply error "incorrect argument"
				     r `(,(cdr d) ,r) caller))))
		     (else
		      (if (string? caller)
			  (error caller d
				 `(or (list? ,d)
				      (and (pair? ,d) (procedure? (cdr ,d)))))
			  (apply error "bad default" d
				 `(or (list? ,d)
				      (and (pair? ,d) (procedure? (cdr ,d))))
				 caller)))))
		  (take rest number) (take default number))
	(apply values
	       (if (> default-length rest-length)
		   (append rest
			   (map (lambda (x)
				  (if (pair? x)
				      (car x)
				      (if (string? caller)
					  (error caller x `(pair? ,x))
					  (apply error "bad default" x
						 `(pair? ,x) caller))))
				(list-tail default rest-length)))
		   rest))))
     (else
      (apply values (if (> default-length rest-length)
			(append rest (list-tail default rest-length))
			rest))))))

(define-syntax arg-and
  (syntax-rules()
    ((arg-and arg (a1 a2 ...) ...)
     (and (or (symbol? 'arg)
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(arg-and arg (a1 a2 ...) ...)))
	  (or (a1 a2 ...)
	      (error "incorrect argument" arg 'arg '(a1 a2 ...)))
	  ...))
    ((arg-and caller arg (a1 a2 ...) ...)
     (and (or (symbol? 'arg)
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(arg-and caller arg (a1 a2 ...) ...)))
	  (or (a1 a2 ...)
	      (if (string? caller)
		  (error caller arg 'arg '(a1 a2 ...))
		  (error "incorrect argument" arg 'arg '(a1 a2 ...) caller)))
	  ...))))

;; accessory macro for arg-ands
(define-syntax caller-arg-and
  (syntax-rules()
    ((caller-arg-and caller arg (a1 a2 ...) ...)
     (and (or (symbol? 'arg)
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(caller-arg-and caller arg (a1 a2 ...) ...)))
	  (or (a1 a2 ...)
	      (if (string? caller)
		  (error caller arg 'arg '(a1 a2 ...))
		  (error "incorrect argument" arg 'arg '(a1 a2 ...) caller)))
	  ...))
    ((caller-arg-and null caller arg (a1 a2 ...) ...)
     (and (or (symbol? 'arg)
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(caller-arg-and caller arg (a1 a2 ...) ...)))
	  (or (a1 a2 ...)
	      (if (string? caller)
		  (error caller arg 'arg '(a1 a2 ...))
		  (error "incorrect argument" arg 'arg '(a1 a2 ...) caller)))
	  ...))))

(define-syntax arg-ands
  (syntax-rules (common)
    ((arg-ands (a1 a2 ...) ...)
     (and (arg-and a1 a2 ...) ...))
    ((arg-ands common caller (a1 a2 ...) ...)
     (and (caller-arg-and caller a1 a2 ...) ...))))

(define-syntax arg-or
  (syntax-rules()
    ((arg-or arg (a1 a2 ...) ...)
     (or (and (not (symbol? 'arg))
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(arg-or arg (a1 a2 ...) ...)))
	 (and (a1 a2 ...)
	      (error "incorrect argument" arg 'arg '(a1 a2 ...)))
	 ...))
    ((arg-or caller arg (a1 a2 ...) ...)
     (or (and (not (symbol? 'arg))
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(arg-or caller arg (a1 a2 ...) ...)))
	 (and (a1 a2 ...)
	      (if (string? caller)
		  (error caller arg 'arg '(a1 a2 ...))
		  (error "incorrect argument" arg 'arg '(a1 a2 ...) caller)))
	 ...))))

;; accessory macro for arg-ors
(define-syntax caller-arg-or
  (syntax-rules()
    ((caller-arg-or caller arg (a1 a2 ...) ...)
     (or (and (not (symbol? 'arg))
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(caller-arg-or caller arg (a1 a2 ...) ...)))
	 (and (a1 a2 ...)
	      (if (string? caller)
		  (error caller arg 'arg '(a1 a2 ...))
		  (error "incorrect argument" arg 'arg '(a1 a2 ...) caller)))
	 ...))
    ((caller-arg-or null caller arg (a1 a2 ...) ...)
     (or (and (not (symbol? 'arg))
	      (error "bad syntax" 'arg '(symbol? 'arg)
		     '(caller-arg-or caller arg (a1 a2 ...) ...)))
	 (and (a1 a2 ...)
	      (if (string? caller)
		  (error caller arg 'arg '(a1 a2 ...))
		  (error "incorrect argument" arg 'arg '(a1 a2 ...) caller)))
	 ...))))

(define-syntax arg-ors
  (syntax-rules (common)
    ((arg-ors (a1 a2 ...) ...)
     (or (arg-or a1 a2 ...) ...))
    ((arg-ors common caller (a1 a2 ...) ...)
     (or (caller-arg-or caller a1 a2 ...) ...))))

(define-syntax err-and
  (syntax-rules ()
    ((err-and err expression ...)
     (and (or expression
	      (if (string? err)
		  (error err 'expression)
		  (error "false expression" 'expression err)))
	  ...))))

(define-syntax err-ands
  (syntax-rules ()
    ((err-ands (err expression ...)  ...)
     (and (err-and err expression ...)
	  ...))))

(define-syntax err-or
  (syntax-rules ()
    ((err-or err expression ...)
     (or (and expression
	      (if (string? err)
		  (error err 'expression)
		  (error "true expression" 'expression err)))
	 ...))))

(define-syntax err-ors
  (syntax-rules ()
    ((err-ors (err expression ...) ...)
     (or (err-or err expression ...)
	 ...))))

Copyright

Copyright (C) Joo ChurlSoo (2004). All Rights Reserved.

This document and translations of it may be copied and furnished to others, and
derivative works that comment on or otherwise explain it or assist in its
implementation may be prepared, copied, published and distributed, in whole or
in part, without restriction of any kind, provided that the above copyright
notice and this paragraph are included on all such copies and derivative works.
However, this document itself may not be modified in any way, such as by
removing the copyright notice or references to the Scheme Request For
Implementation process or editors, except as needed for the purpose of
developing SRFIs in which case the procedures for copyrights defined in the
SRFI process must be followed, or as required to translate it into languages
other than English.

The limited permissions granted above are perpetual and will not be revoked by
the authors or their successors or assigns.

This document and the information contained herein is provided on an "AS IS"
basis and THE AUTHOR AND THE SRFI EDITORS DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.