srfi-1.scm

Scheme跨平台编译器

;;;; srfi-1.scm - Shivers' reference implementation of SRFI-1


; Some things to make it work with CHICKEN: (flw)
;

(declare
  (unit srfi-1)
  (disable-interrupts)
  (disable-warning redef)
  (hide ##srfi1#cars+cdrs/no-test ##srfi1#cdrs ##srfi1#cars+ ##srfi1#really-append-map ##srfi1#cars+cdrs+
	##srfi1#cars+cdrs ##srfi1#lset2<=)
  (extended-bindings)
  (standard-bindings not boolean? apply call-with-current-continuation eq? eqv? equal? pair? cons car cdr caar cadr
		     cdar cddr caaar caadr cadar caddr cdaar cdadr cddar cdddr caaaar caaadr caadar caaddr cadaar
		     cadadr caddar cadddr cdaaar cdaadr cdadar cdaddr cddaar cddadr cdddar cddddr set-car! set-cdr!
		     null? list list? length zero? * - error + / - > < >= <= current-output-port current-input-port
		     write-char newline write display append symbol->string char? char->integer
		     integer->char eof-object? vector-length string-length string-ref string-set! vector-ref 
		     vector-set! char=? char<? char>? char>=? char<=? gcd lcm reverse symbol? string->symbol
		     number? complex? real? integer? rational? odd? even? positive? negative? exact? inexact?
		     max min quotient remainder modulo floor ceiling truncate round exact->inexact inexact->exact
		     exp log sin expt sqrt cos tan asin acos atan number->string string->number char-ci=?
		     char-ci<? char-ci>? char-ci>=? char-ci<=? char-alphabetic? char-whitespace? char-numeric?
		     char-lower-case? char-upper-case? char-upcase char-downcase string? string=? string>? string<?
		     string>=? string<=? string-ci=? string-ci<? string-ci>? string-ci<=? string-ci>=?
		     string-append string->list list->string vector? vector->list list->vector string read
		     read-char substring string-fill! vector-fill! make-string make-vector open-input-file
		     open-output-file call-with-input-file call-with-output-file close-input-port close-output-port
		     port? values call-with-values vector procedure? memq memv assq assv) )

(cond-expand
 [paranoia]
 [else
  (declare
    (no-procedure-checks-for-usual-bindings)
    (bound-to-procedure 
     every any partition! reduce lset-difference! append! pair-fold lset-diff+intersection! fold
     lset-difference filter! filter delete span! span find-tail find delete! pair-for-each car+cdr
     reduce-right last-pair drop)
    (no-bound-checks) ) ] )

(cond-expand
 [unsafe
  (eval-when (compile)
    (define-macro (##sys#check-structure . _) '(##core#undefined))
    (define-macro (##sys#check-range . _) '(##core#undefined))
    (define-macro (##sys#check-pair . _) '(##core#undefined))
    (define-macro (##sys#check-list . _) '(##core#undefined))
    (define-macro (##sys#check-symbol . _) '(##core#undefined))
    (define-macro (##sys#check-string . _) '(##core#undefined))
    (define-macro (##sys#check-char . _) '(##core#undefined))
    (define-macro (##sys#check-exact . _) '(##core#undefined))
    (define-macro (##sys#check-port . _) '(##core#undefined))
    (define-macro (##sys#check-number . _) '(##core#undefined))
    (define-macro (##sys#check-byte-vector . _) '(##core#undefined)) ) ]
 [else
  (declare (emit-exports "srfi-1.exports"))] )

(register-feature! 'srfi-1)

(eval-when (compile eval)
  (define-macro (:optional arg default)
    (let ([var (gensym)])
      `(let ((,var ,arg))
	 (if (null? ,var)
	     ,default
	     (car ,var) ) ) ) ) )


;;; SRFI-1 list-processing library 			-*- Scheme -*-
;;; Reference implementation
;;;
;;; Copyright (c) 1998, 1999 by Olin Shivers. You may do as you please with
;;; this code as long as you do not remove this copyright notice or
;;; hold me liable for its use. Please send bug reports to [e-mail].
;;;     -Olin

;;; This is a library of list- and pair-processing functions. I wrote it after
;;; carefully considering the functions provided by the libraries found in
;;; R4RS/R5RS Scheme, MIT Scheme, Gambit, RScheme, MzScheme, slib, Common
;;; Lisp, Bigloo, guile, T, APL and the SML standard basis. It is a pretty
;;; rich toolkit, providing a superset of the functionality found in any of
;;; the various Schemes I considered.

;;; This implementation is intended as a portable reference implementation
;;; for SRFI-1. See the porting notes below for more information.

;;; Exported:
;;; xcons tree-copy make-list list-tabulate cons* list-copy 
;;; proper-list? circular-list? dotted-list? not-pair? null-list? list=
;;; circular-list length+
;;; iota
;;; first second third fourth fifth sixth seventh eighth ninth tenth
;;; car+cdr
;;; take       drop       
;;; take-right drop-right 
;;; take!      drop-right!
;;; split-at   split-at!
;;; last last-pair
;;; zip unzip1 unzip2 unzip3 unzip4 unzip5
;;; count
;;; append! append-reverse append-reverse! concatenate concatenate! 
;;; unfold       fold       pair-fold       reduce
;;; unfold-right fold-right pair-fold-right reduce-right
;;; append-map append-map! map! pair-for-each filter-map map-in-order
;;; filter  partition  remove
;;; filter! partition! remove! 
;;; find find-tail any every list-index
;;; take-while drop-while take-while!
;;; span break span! break!

;;; In principle, the following R4RS list- and pair-processing procedures
;;; are also part of this package's exports, although they are not defined
;;; in this file:
;;;   Primitives: cons pair? null? car cdr set-car! set-cdr!
;;;   Non-primitives: list length append reverse cadr ... cddddr list-ref
;;;                   memq memv assq assv
;;;   (The non-primitives are defined in this file, but commented out.)
;;;
;;; These R4RS procedures have extended definitions in SRFI-1 and are defined
;;; in this file:
;;;   map for-each member assoc
;;;
;;; The remaining two R4RS list-processing procedures are not included: 
;;;   list-tail (use drop)
;;;   list? (use proper-list?)


;;; A note on recursion and iteration/reversal:
;;; Many iterative list-processing algorithms naturally compute the elements
;;; of the answer list in the wrong order (left-to-right or head-to-tail) from
;;; the order needed to cons them into the proper answer (right-to-left, or
;;; tail-then-head). One style or idiom of programming these algorithms, then,
;;; loops, consing up the elements in reverse order, then destructively 
;;; reverses the list at the end of the loop. I do not do this. The natural
;;; and efficient way to code these algorithms is recursively. This trades off
;;; intermediate temporary list structure for intermediate temporary stack
;;; structure. In a stack-based system, this improves cache locality and
;;; lightens the load on the GC system. Don't stand on your head to iterate!
;;; Recurse, where natural. Multiple-value returns make this even more
;;; convenient, when the recursion/iteration has multiple state values.

;;; Porting:
;;; This is carefully tuned code; do not modify casually.
;;;   - It is careful to share storage when possible;
;;;   - Side-effecting code tries not to perform redundant writes.
;;; 
;;; That said, a port of this library to a specific Scheme system might wish
;;; to tune this code to exploit particulars of the implementation. 
;;; The single most important compiler-specific optimisation you could make
;;; to this library would be to add rewrite rules or transforms to:
;;; - transform applications of n-ary procedures (e.g. LIST=, CONS*, APPEND,
;;;   LSET-UNION) into multiple applications of a primitive two-argument 
;;;   variant.
;;; - transform applications of the mapping functions (MAP, FOR-EACH, FOLD, 
;;;   ANY, EVERY) into open-coded loops. The killer here is that these 
;;;   functions are n-ary. Handling the general case is quite inefficient,
;;;   requiring many intermediate data structures to be allocated and
;;;   discarded.
;;; - transform applications of procedures that take optional arguments
;;;   into calls to variants that do not take optional arguments. This
;;;   eliminates unnecessary consing and parsing of the rest parameter.
;;;
;;; These transforms would provide BIG speedups. In particular, the n-ary
;;; mapping functions are particularly slow and cons-intensive, and are good
;;; candidates for tuning. I have coded fast paths for the single-list cases,
;;; but what you really want to do is exploit the fact that the compiler
;;; usually knows how many arguments are being passed to a particular
;;; application of these functions -- they are usually explicitly called, not
;;; passed around as higher-order values. If you can arrange to have your
;;; compiler produce custom code or custom linkages based on the number of
;;; arguments in the call, you can speed these functions up a *lot*. But this
;;; kind of compiler technology no longer exists in the Scheme world as far as
;;; I can see.
;;;
;;; Note that this code is, of course, dependent upon standard bindings for
;;; the R5RS procedures -- i.e., it assumes that the variable CAR is bound
;;; to the procedure that takes the car of a list. If your Scheme 
;;; implementation allows user code to alter the bindings of these procedures
;;; in a manner that would be visible to these definitions, then there might
;;; be trouble. You could consider horrible kludgery along the lines of
;;;    (define fact 
;;;      (let ((= =) (- -) (* *))
;;;        (letrec ((real-fact (lambda (n) 
;;;                              (if (= n 0) 1 (* n (real-fact (- n 1)))))))
;;;          real-fact)))
;;; Or you could consider shifting to a reasonable Scheme system that, say,
;;; has a module system protecting code from this kind of lossage.
;;;
;;; This code does a fair amount of run-time argument checking. If your
;;; Scheme system has a sophisticated compiler that can eliminate redundant
;;; error checks, this is no problem. However, if not, these checks incur
;;; some performance overhead -- and, in a safe Scheme implementation, they
;;; are in some sense redundant: if we don't check to see that the PROC 
;;; parameter is a procedure, we'll find out anyway three lines later when
;;; we try to call the value. It's pretty easy to rip all this argument 
;;; checking code out if it's inappropriate for your implementation -- just
;;; nuke every call to CHECK-ARG.
;;;
;;; On the other hand, if you *do* have a sophisticated compiler that will
;;; actually perform soft-typing and eliminate redundant checks (Rice's systems
;;; being the only possible candidate of which I'm aware), leaving these checks 
;;; in can *help*, since their presence can be elided in redundant cases,
;;; and in cases where they are needed, performing the checks early, at
;;; procedure entry, can "lift" a check out of a loop. 
;;;
;;; Finally, I have only checked the properties that can portably be checked
;;; with R5RS Scheme -- and this is not complete. You may wish to alter
;;; the CHECK-ARG parameter checks to perform extra, implementation-specific
;;; checks, such as procedure arity for higher-order values.
;;;
;;; The code has only these non-R4RS dependencies:
;;;   A few calls to an ERROR procedure;
;;;   Uses of the R5RS multiple-value procedure VALUES and the m-v binding
;;;     RECEIVE macro (which isn't R5RS, but is a trivial macro).
;;;   Many calls to a parameter-checking procedure check-arg:
;;;    (define (check-arg pred val caller)
;;;      (let lp ((val val))
;;;        (if (pred val) val (lp (error "Bad argument" val pred caller)))))
;;;   A few uses of the LET-OPTIONAL and :OPTIONAL macros for parsing
;;;     optional arguments.
;;;
;;; Most of these procedures use the NULL-LIST? test to trigger the
;;; base case in the inner loop or recursion. The NULL-LIST? function
;;; is defined to be a careful one -- it raises an error if passed a
;;; non-nil, non-pair value. The spec allows an implementation to use
;;; a less-careful implementation that simply defines NULL-LIST? to
;;; be NOT-PAIR?. This would speed up the inner loops of these procedures
;;; at the expense of having them silently accept dotted lists.

;;; A note on dotted lists:
;;; I, personally, take the view that the only consistent view of lists
;;; in Scheme is the view that *everything* is a list -- values such as
;;; 3 or "foo" or 'bar are simply empty dotted lists. This is due to the
;;; fact that Scheme actually has no true list type. It has a pair type,
;;; and there is an *interpretation* of the trees built using this type
;;; as lists.
;;;
;;; I lobbied to have these list-processing procedures hew to this
;;; view, and accept any value as a list argument. I was overwhelmingly
;;; overruled during the SRFI discussion phase. So I am inserting this
;;; text in the reference lib and the SRFI spec as a sort of "minority
;;; opinion" dissent.
;;;
;;; Many of the procedures in this library can be trivially redefined
;;; to handle dotted lists, just by changing the NULL-LIST? base-case
;;; check to NOT-PAIR?, meaning that any non-pair value is taken to be
;;; an empty list. For most of these procedures, that's all that is
;;; required.
;;;
;;; However, we have to do a little more work for some procedures that
;;; *produce* lists from other lists.  Were we to extend these procedures to
;;; accept dotted lists, we would have to define how they terminate the lists
;;; produced as results when passed a dotted list. I designed a coherent set
;;; of termination rules for these cases; this was posted to the SRFI-1
;;; discussion list. I additionally wrote an earlier version of this library
;;; that implemented that spec. It has been discarded during later phases of
;;; the definition and implementation of this library.
;;;
;;; The argument *against* defining these procedures to work on dotted
;;; lists is that dotted lists are the rare, odd case, and that by 
;;; arranging for the procedures to handle them, we lose error checking
;;; in the cases where a dotted list is passed by accident -- e.g., when
;;; the programmer swaps a two arguments to a list-processing function,
;;; one being a scalar and one being a list. For example,
;;;     (member '(1 3 5 7 9) 7)
;;; This would quietly return #f if we extended MEMBER to accept dotted
;;; lists.
;;;
;;; The SRFI discussion record contains more discussion on this topic.


;;; Constructors
;;;;;;;;;;;;;;;;

;;; Occasionally useful as a value to be passed to a fold or other
;;; higher-order procedure.
(define (xcons d a) (cons a d))

;;;; Recursively copy every cons.
;(define (tree-copy x)
;  (let recur ((x x))
;    (if (not (pair? x)) x
;	(cons (recur (car x)) (recur (cdr x))))))

;;; Make a list of length LEN.

(define (make-list len . maybe-elt)
;  (check-arg (lambda (n) (and (integer? n) (>= n 0))) len make-list)
  (##sys#check-exact len 'make-list)
  (let ((elt (cond ((null? maybe-elt) #f) ; Default value
		   ((null? (cdr maybe-elt)) (car maybe-elt))
		   (else (##sys#error 'make-list "Too many arguments to MAKE-LIST"
				(cons len maybe-elt))))))
    (do ((i len (fx- i 1))
	 (ans '() (cons elt ans)))
	((fx<= i 0) ans))))


;(define (list . ans) ans)	; R4RS


;;; Make a list of length LEN. Elt i is (PROC i) for 0 <= i < LEN.

(define (list-tabulate len proc)
;  (check-arg (lambda (n) (and (integer? n) (>= n 0))) len list-tabulate)
;  (check-arg procedure? proc list-tabulate)
  (##sys#check-exact len 'list-tabulate)
  (do ((i (fx- len 1) (fx- i 1))
       (ans '() (cons (proc i) ans)))
      ((fx< i 0) ans)))

;;; (cons* a1 a2 ... an) = (cons a1 (cons a2 (cons ... an)))
;;; (cons* a1) = a1	(cons* a1 a2 ...) = (cons a1 (cons* a2 ...))
;;;
;;; (cons first (unfold not-pair? car cdr rest values))

(define (cons* first . rest)
  (let recur ((x first) (rest rest))
    (if (pair? rest)
	(cons x (recur (car rest) (cdr rest)))
	x)))

;;; (unfold not-pair? car cdr lis values)

(define (list-copy lis)				
  (let recur ((lis lis))			
    (if (pair? lis)				
	(cons (car lis) (recur (cdr lis)))	
	lis)))					

;;; IOTA count [start step]	(start start+step ... start+(count-1)*step)

(define (iota count . maybe-start+step)
;  (check-arg integer? count iota)
  (##sys#check-number count 'iota)
  (if (< count 0) (##sys#error 'iota "Negative step count" iota count))
  (let ((start (:optional maybe-start+step 0))
	(step (if (pair? maybe-start+step)
		  (:optional (cdr maybe-start+step) 1)
		  1) ) )
    (##sys#check-number start 'iota)
    (##sys#check-number step 'iota)
;    (check-arg number? start iota)
;    (check-arg number? step iota)
    (let ((last-val (+ start (* (- count 1) step))))
      (do ((count count (- count 1))
	   (val last-val (- val step))
	   (ans '() (cons val ans)))
	  ((<= count 0)  ans)))))
	  
;;; I thought these were lovely, but the public at large did not share my
;;; enthusiasm...
;;; :IOTA to		(0 ... to-1)
;;; :IOTA from to	(from ... to-1)
;;; :IOTA from to step  (from from+step ...)

;;; IOTA: to		(1 ... to)
;;; IOTA: from to	(from+1 ... to)
;;; IOTA: from to step	(from+step from+2step ...)

;(define (##srfi1#parse-iota-args arg1 rest-args proc)
;  (let ((check (lambda (n) (check-arg integer? n proc))))
;    (check arg1)
;    (if (pair? rest-args)
;	(let ((arg2 (check (car rest-args)))
;	      (rest (cdr rest-args)))
;	  (if (pair? rest)
;	      (let ((arg3 (check (car rest)))
;		    (rest (cdr rest)))
;		(if (pair? rest) (error "Too many parameters" proc arg1 rest-args)
;		    (values arg1 arg2 arg3)))
;	      (values arg1 arg2 1)))
;	(values 0 arg1 1))))
;
;(define (iota: arg1 . rest-args)
;  (receive (from to step) (##srfi1#parse-iota-args arg1 rest-args iota:)
;    (let* ((numsteps (floor (/ (- to from) step)))
;	   (last-val (+ from (* step numsteps))))
;      (if (< numsteps 0) (error "Negative step count" iota: from to step))
;      (do ((steps-left numsteps (- steps-left 1))
;	   (val last-val (- val step))
;	   (ans '() (cons val ans)))
;	  ((<= steps-left 0) ans)))))
;
;
;(define (:iota arg1 . rest-args)
;  (receive (from to step) (##srfi1#parse-iota-args arg1 rest-args :iota)
;    (let* ((numsteps (ceiling (/ (- to from) step)))
;	   (last-val (+ from (* step (- numsteps 1)))))
;      (if (< numsteps 0) (error "Negative step count" :iota from to step))
;      (do ((steps-left numsteps (- steps-left 1))
;	   (val last-val (- val step))
;	   (ans '() (cons val ans)))
;	  ((<= steps-left 0) ans)))))



(define (circular-list val1 . vals)
  (let ((ans (cons val1 vals)))
    (set-cdr! (last-pair ans) ans)
    ans))

;;; <proper-list> ::= ()			; Empty proper list
;;;		  |   (cons <x> <proper-list>)	; Proper-list pair
;;; Note that this definition rules out circular lists -- and this
;;; function is required to detect this case and return false.

(define proper-list? list?)

#;(define (proper-list? x)
  (let lp ((x x) (lag x))
    (if (pair? x)
	(let ((x (cdr x)))
	  (if (pair? x)
	      (let ((x   (cdr x))
		    (lag (cdr lag)))