== SRFI-51: Handling rest list === Related SRFIs The procedure and macros proposed in this SRFI make a strong combination with {{RECEIVE}} ([[https://srfi.schemers.org/srfi-8/|SRFI 8]]) and {{LET-VALUES}} ([[https://srfi.schemers.org/srfi-11/|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, 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, and eight macros which additionally check the rest arguments that are returned by {{REST-VALUES}}. === Rationale When defining a procedure with a variable number of arguments, {{REST-VALUES}} with or without the checking macros reduces the clutter of various conditionals and error conditions. === Specification ==== REST-VALUES (REST-VALUES [] [ ...]) {{}} is any scheme expression. {{}} should be an integer, +, -, or a boolean. * 1. When the {{}} is + or a positive integer, each {{}} should be a list that contains default value(s), or a pair whose car is a default value and cdr is a predicate procedure. * 2. When the {{}} is - or a negative integer, each {{}} is any scheme expression. * 3. When the {{}} is a boolean, each {{}} is the same as 1. * 1. (first mode of operation) {{REST-VALUES}} checks whether each element of the {{}} is a member of the corresponding {{}} list, or satisfies the predicate procedure of the corresponding {{}} 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 {{}}, then {{REST-VALUES}} additionally returns the car values of the remaining {{}}s. On the other hand, when the number of elements of the {{}} are more than the number of the {{}}s, the supernumerary elements are additionally returned if the {{}} is +, or its value is not less than the number of elements of the {{}}. * 2. (second mode of operation) This is the same as the first except that {{REST-VALUES}} does not check each element of the {{}}, and it uses - instead of +, and an absolute value instead of a simple value as the value of {{}}. 3. (third mode of operation) {{REST-VALUES}} checks whether any element of the {{}} list is a member of the {{}}, or any element of the {{}} satisfies the predicate procedure of the {{}} pair, and then returns the checked element. If the {{}} doesn't pass, {{REST-VALUES}} returns the car value of the {{}}. When any elements of the {{}} are remained after the above processing, {{REST-VALUES}} either signals an error if the {{}} is {{#t}}, or returns the remaining elements of the {{}} if the {{}} is {{#f}}. ==== ARG and END procedures (ARG-AND [] ...) (ARG-ANDS [COMMON ] ([] ...) ...) (ERR-AND ...) (ERR-ANDS ( ...) ...) (ARG-OR [] ...) (ARG-ORS [COMMON ] ([] ...) ...) (ERR-OR ...) (ERR-ORS ( ...) ...) * Each {{}} should be an argument of a procedure. * The {{}}, {{}}, and {{}} are any scheme expressions, but the {{}} should contain the corresponding {{}}. {{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 => 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 1) => error too many defaults (y 3 1) default-list (<= (length default-list) 2) (rest-values 'caller rest-list 1 '(x y z)) => error too many arguments (x 1) rest-list (<= (length rest-list) 1) caller (rest-values caller rest-list 2 (list 'x 'y 'z) (cons "str" string?)) => error incorrect argument 1 arg ( arg) (rest-values rest-list 2 '(y z) `(100 . ,number?)) => error unmatched argument x arg (member arg (y z)) (rest-values "caller: bad argument" rest-list 2 '(y z) `(100 . ,number?)) => error caller: bad argument x arg (member arg (y z)) (rest-values 'caller rest-list (list 'x 'y) (cons 1 number?)) => error bad optional argument (x y) option (or (boolean? option) (integer? option) (memq option (list + -))) caller (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) rest-list (null? rest-list) (rest-values rest-list #f `(100 . ,number?) `("str" . ,string?) `(y z)) => 1 "str" y x 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) (arg-and 'caller num (number? num) (< num 2)) => error incorrect argument 2 num (< num 2) caller (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: 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 ( ). (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 ( ) or ( ). (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))) ...))) (define (procedure-with-sequential-binding-arguments . a-b-c) (receive (a b c) (rest-values a-b-c -3 10 #f #f) (let* ((b (or b (+ a 10))) (c (or c (+ a b)))) ...))) === Author * Joo ChurlSoo * Ported to Chicken Scheme 5 by Sergey Goldgaber === Version history ==== [[https://github.com/diamond-lizard/srfi-51/releases/tag/0.2|0.2]] - Fixed missing exports ==== [[https://github.com/diamond-lizard/srfi-51/releases/tag/0.1|0.1]] - Ported to Chicken Scheme 5 === Copyright Copyright (C) Joo ChurlSoo (2004). All Rights Reserved. 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