Author: yamakenz Date: Thu Jun 14 14:14:00 2007 New Revision: 4593 Added: vendor/misc/srfi-1-reference.scm Modified: vendor/misc/README
Log: * vendor/misc/srfi-1-reference.scm - New file imported from http://srfi.schemers.org/srfi-1/srfi-1-reference.scm * vendor/misc/README - Update Modified: vendor/misc/README ============================================================================== --- vendor/misc/README (original) +++ vendor/misc/README Thu Jun 14 14:14:00 2007 @@ -9,3 +9,11 @@ Unless specified otherwise, all the code and the documentation on this site is in public domain. ------------------------------------------------------------------------------ +File: srfi-1-reference.scm +URL: http://srfi.schemers.org/srfi-1/srfi-1-reference.scm +License type: MIT like +License terms: + 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 [EMAIL PROTECTED] +------------------------------------------------------------------------------ Added: vendor/misc/srfi-1-reference.scm ============================================================================== --- (empty file) +++ vendor/misc/srfi-1-reference.scm Thu Jun 14 14:14:00 2007 @@ -0,0 +1,1594 @@ +;;; 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 [EMAIL PROTECTED] +;;; -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! +;;; delete delete! +;;; alist-cons alist-copy +;;; delete-duplicates delete-duplicates! +;;; alist-delete alist-delete! +;;; reverse! +;;; lset<= lset= lset-adjoin +;;; lset-union lset-intersection lset-difference lset-xor lset-diff+intersection +;;; lset-union! lset-intersection! lset-difference! lset-xor! lset-diff+intersection! +;;; +;;; 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) + (let ((elt (cond ((null? maybe-elt) #f) ; Default value + ((null? (cdr maybe-elt)) (car maybe-elt)) + (else (error "Too many arguments to MAKE-LIST" + (cons len maybe-elt)))))) + (do ((i len (- i 1)) + (ans '() (cons elt ans))) + ((<= 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) + (do ((i (- len 1) (- i 1)) + (ans '() (cons (proc i) ans))) + ((< 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) + (if (< count 0) (error "Negative step count" iota count)) + (let-optionals maybe-start+step ((start 0) (step 1)) + (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 (%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) (%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) (%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? x) + (let lp ((x x) (lag x)) + (if (pair? x) + (let ((x (cdr x))) + (if (pair? x) + (let ((x (cdr x)) + (lag (cdr lag))) + (and (not (eq? x lag)) (lp x lag))) + (null? x))) + (null? x)))) + + +;;; A dotted list is a finite list (possibly of length 0) terminated +;;; by a non-nil value. Any non-cons, non-nil value (e.g., "foo" or 5) +;;; is a dotted list of length 0. +;;; +;;; <dotted-list> ::= <non-nil,non-pair> ; Empty dotted list +;;; | (cons <x> <dotted-list>) ; Proper-list pair + +(define (dotted-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))) + (and (not (eq? x lag)) (lp x lag))) + (not (null? x)))) + (not (null? x))))) + +(define (circular-list? x) + (let lp ((x x) (lag x)) + (and (pair? x) + (let ((x (cdr x))) + (and (pair? x) + (let ((x (cdr x)) + (lag (cdr lag))) + (or (eq? x lag) (lp x lag)))))))) + +(define (not-pair? x) (not (pair? x))) ; Inline me. + +;;; This is a legal definition which is fast and sloppy: +;;; (define null-list? not-pair?) +;;; but we'll provide a more careful one: +(define (null-list? l) + (cond ((pair? l) #f) + ((null? l) #t) + (else (error "null-list?: argument out of domain" l)))) + + +(define (list= = . lists) + (or (null? lists) ; special case + + (let lp1 ((list-a (car lists)) (others (cdr lists))) + (or (null? others) + (let ((list-b (car others)) + (others (cdr others))) + (if (eq? list-a list-b) ; EQ? => LIST= + (lp1 list-b others) + (let lp2 ((list-a list-a) (list-b list-b)) + (if (null-list? list-a) + (and (null-list? list-b) + (lp1 list-b others)) + (and (not (null-list? list-b)) + (= (car list-a) (car list-b)) + (lp2 (cdr list-a) (cdr list-b))))))))))) + + + +;;; R4RS, so commented out. +;(define (length x) ; LENGTH may diverge or +; (let lp ((x x) (len 0)) ; raise an error if X is +; (if (pair? x) ; a circular list. This version +; (lp (cdr x) (+ len 1)) ; diverges. +; len))) + +(define (length+ x) ; Returns #f if X is circular. + (let lp ((x x) (lag x) (len 0)) + (if (pair? x) + (let ((x (cdr x)) + (len (+ len 1))) + (if (pair? x) + (let ((x (cdr x)) + (lag (cdr lag)) + (len (+ len 1))) + (and (not (eq? x lag)) (lp x lag len))) + len)) + len))) + +(define (zip list1 . more-lists) (apply map list list1 more-lists)) + + +;;; Selectors +;;;;;;;;;;;;; + +;;; R4RS non-primitives: +;(define (caar x) (car (car x))) +;(define (cadr x) (car (cdr x))) +;(define (cdar x) (cdr (car x))) +;(define (cddr x) (cdr (cdr x))) +; +;(define (caaar x) (caar (car x))) +;(define (caadr x) (caar (cdr x))) +;(define (cadar x) (cadr (car x))) +;(define (caddr x) (cadr (cdr x))) +;(define (cdaar x) (cdar (car x))) +;(define (cdadr x) (cdar (cdr x))) +;(define (cddar x) (cddr (car x))) +;(define (cdddr x) (cddr (cdr x))) +; +;(define (caaaar x) (caaar (car x))) +;(define (caaadr x) (caaar (cdr x))) +;(define (caadar x) (caadr (car x))) +;(define (caaddr x) (caadr (cdr x))) +;(define (cadaar x) (cadar (car x))) +;(define (cadadr x) (cadar (cdr x))) +;(define (caddar x) (caddr (car x))) +;(define (cadddr x) (caddr (cdr x))) +;(define (cdaaar x) (cdaar (car x))) +;(define (cdaadr x) (cdaar (cdr x))) +;(define (cdadar x) (cdadr (car x))) +;(define (cdaddr x) (cdadr (cdr x))) +;(define (cddaar x) (cddar (car x))) +;(define (cddadr x) (cddar (cdr x))) +;(define (cdddar x) (cdddr (car x))) +;(define (cddddr x) (cdddr (cdr x))) + + +(define first car) +(define second cadr) +(define third caddr) +(define fourth cadddr) +(define (fifth x) (car (cddddr x))) +(define (sixth x) (cadr (cddddr x))) +(define (seventh x) (caddr (cddddr x))) +(define (eighth x) (cadddr (cddddr x))) +(define (ninth x) (car (cddddr (cddddr x)))) +(define (tenth x) (cadr (cddddr (cddddr x)))) + +(define (car+cdr pair) (values (car pair) (cdr pair))) + +;;; take & drop + +(define (take lis k) + (check-arg integer? k take) + (let recur ((lis lis) (k k)) + (if (zero? k) '() + (cons (car lis) + (recur (cdr lis) (- k 1)))))) + +(define (drop lis k) + (check-arg integer? k drop) + (let iter ((lis lis) (k k)) + (if (zero? k) lis (iter (cdr lis) (- k 1))))) + +(define (take! lis k) + (check-arg integer? k take!) + (if (zero? k) '() + (begin (set-cdr! (drop lis (- k 1)) '()) + lis))) + +;;; TAKE-RIGHT and DROP-RIGHT work by getting two pointers into the list, +;;; off by K, then chasing down the list until the lead pointer falls off +;;; the end. + +(define (take-right lis k) + (check-arg integer? k take-right) + (let lp ((lag lis) (lead (drop lis k))) + (if (pair? lead) + (lp (cdr lag) (cdr lead)) + lag))) + +(define (drop-right lis k) + (check-arg integer? k drop-right) + (let recur ((lag lis) (lead (drop lis k))) + (if (pair? lead) + (cons (car lag) (recur (cdr lag) (cdr lead))) + '()))) + +;;; In this function, LEAD is actually K+1 ahead of LAG. This lets +;;; us stop LAG one step early, in time to smash its cdr to (). +(define (drop-right! lis k) + (check-arg integer? k drop-right!) + (let ((lead (drop lis k))) + (if (pair? lead) + + (let lp ((lag lis) (lead (cdr lead))) ; Standard case + (if (pair? lead) + (lp (cdr lag) (cdr lead)) + (begin (set-cdr! lag '()) + lis))) + + '()))) ; Special case dropping everything -- no cons to side-effect. + +;(define (list-ref lis i) (car (drop lis i))) ; R4RS + +;;; These use the APL convention, whereby negative indices mean +;;; "from the right." I liked them, but they didn't win over the +;;; SRFI reviewers. +;;; K >= 0: Take and drop K elts from the front of the list. +;;; K <= 0: Take and drop -K elts from the end of the list. + +;(define (take lis k) +; (check-arg integer? k take) +; (if (negative? k) +; (list-tail lis (+ k (length lis))) +; (let recur ((lis lis) (k k)) +; (if (zero? k) '() +; (cons (car lis) +; (recur (cdr lis) (- k 1))))))) +; +;(define (drop lis k) +; (check-arg integer? k drop) +; (if (negative? k) +; (let recur ((lis lis) (nelts (+ k (length lis)))) +; (if (zero? nelts) '() +; (cons (car lis) +; (recur (cdr lis) (- nelts 1))))) +; (list-tail lis k))) +; +; +;(define (take! lis k) +; (check-arg integer? k take!) +; (cond ((zero? k) '()) +; ((positive? k) +; (set-cdr! (list-tail lis (- k 1)) '()) +; lis) +; (else (list-tail lis (+ k (length lis)))))) +; +;(define (drop! lis k) +; (check-arg integer? k drop!) +; (if (negative? k) +; (let ((nelts (+ k (length lis)))) +; (if (zero? nelts) '() +; (begin (set-cdr! (list-tail lis (- nelts 1)) '()) +; lis))) +; (list-tail lis k))) + +(define (split-at x k) + (check-arg integer? k split-at) + (let recur ((lis x) (k k)) + (if (zero? k) (values '() lis) + (receive (prefix suffix) (recur (cdr lis) (- k 1)) + (values (cons (car lis) prefix) suffix))))) + +(define (split-at! x k) + (check-arg integer? k split-at!) + (if (zero? k) (values '() x) + (let* ((prev (drop x (- k 1))) + (suffix (cdr prev))) + (set-cdr! prev '()) + (values x suffix)))) + + +(define (last lis) (car (last-pair lis))) + +(define (last-pair lis) + (check-arg pair? lis last-pair) + (let lp ((lis lis)) + (let ((tail (cdr lis))) + (if (pair? tail) (lp tail) lis)))) + + +;;; Unzippers -- 1 through 5 +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(define (unzip1 lis) (map car lis)) + +(define (unzip2 lis) + (let recur ((lis lis)) + (if (null-list? lis) (values lis lis) ; Use NOT-PAIR? to handle + (let ((elt (car lis))) ; dotted lists. + (receive (a b) (recur (cdr lis)) + (values (cons (car elt) a) + (cons (cadr elt) b))))))) + +(define (unzip3 lis) + (let recur ((lis lis)) + (if (null-list? lis) (values lis lis lis) + (let ((elt (car lis))) + (receive (a b c) (recur (cdr lis)) + (values (cons (car elt) a) + (cons (cadr elt) b) + (cons (caddr elt) c))))))) + +(define (unzip4 lis) + (let recur ((lis lis)) + (if (null-list? lis) (values lis lis lis lis) + (let ((elt (car lis))) + (receive (a b c d) (recur (cdr lis)) + (values (cons (car elt) a) + (cons (cadr elt) b) + (cons (caddr elt) c) + (cons (cadddr elt) d))))))) + +(define (unzip5 lis) + (let recur ((lis lis)) + (if (null-list? lis) (values lis lis lis lis lis) + (let ((elt (car lis))) + (receive (a b c d e) (recur (cdr lis)) + (values (cons (car elt) a) + (cons (cadr elt) b) + (cons (caddr elt) c) + (cons (cadddr elt) d) + (cons (car (cddddr elt)) e))))))) + + +;;; append! append-reverse append-reverse! concatenate concatenate! +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(define (append! . lists) + ;; First, scan through lists looking for a non-empty one. + (let lp ((lists lists) (prev '())) + (if (not (pair? lists)) prev + (let ((first (car lists)) + (rest (cdr lists))) + (if (not (pair? first)) (lp rest first) + + ;; Now, do the splicing. + (let lp2 ((tail-cons (last-pair first)) + (rest rest)) + (if (pair? rest) + (let ((next (car rest)) + (rest (cdr rest))) + (set-cdr! tail-cons next) + (lp2 (if (pair? next) (last-pair next) tail-cons) + rest)) + first))))))) + +;;; APPEND is R4RS. +;(define (append . lists) +; (if (pair? lists) +; (let recur ((list1 (car lists)) (lists (cdr lists))) +; (if (pair? lists) +; (let ((tail (recur (car lists) (cdr lists)))) +; (fold-right cons tail list1)) ; Append LIST1 & TAIL. +; list1)) +; '())) + +;(define (append-reverse rev-head tail) (fold cons tail rev-head)) + +;(define (append-reverse! rev-head tail) +; (pair-fold (lambda (pair tail) (set-cdr! pair tail) pair) +; tail +; rev-head)) + +;;; Hand-inline the FOLD and PAIR-FOLD ops for speed. + +(define (append-reverse rev-head tail) + (let lp ((rev-head rev-head) (tail tail)) + (if (null-list? rev-head) tail + (lp (cdr rev-head) (cons (car rev-head) tail))))) + +(define (append-reverse! rev-head tail) + (let lp ((rev-head rev-head) (tail tail)) + (if (null-list? rev-head) tail + (let ((next-rev (cdr rev-head))) + (set-cdr! rev-head tail) + (lp next-rev rev-head))))) + + +(define (concatenate lists) (reduce-right append '() lists)) +(define (concatenate! lists) (reduce-right append! '() lists)) + +;;; Fold/map internal utilities +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;;; These little internal utilities are used by the general +;;; fold & mapper funs for the n-ary cases . It'd be nice if they got inlined. +;;; One the other hand, the n-ary cases are painfully inefficient as it is. +;;; An aggressive implementation should simply re-write these functions +;;; for raw efficiency; I have written them for as much clarity, portability, +;;; and simplicity as can be achieved. +;;; +;;; I use the dreaded call/cc to do local aborts. A good compiler could +;;; handle this with extreme efficiency. An implementation that provides +;;; a one-shot, non-persistent continuation grabber could help the compiler +;;; out by using that in place of the call/cc's in these routines. +;;; +;;; These functions have funky definitions that are precisely tuned to +;;; the needs of the fold/map procs -- for example, to minimize the number +;;; of times the argument lists need to be examined. + +;;; Return (map cdr lists). +;;; However, if any element of LISTS is empty, just abort and return '(). +(define (%cdrs lists) + (call-with-current-continuation + (lambda (abort) + (let recur ((lists lists)) + (if (pair? lists) + (let ((lis (car lists))) + (if (null-list? lis) (abort '()) + (cons (cdr lis) (recur (cdr lists))))) + '()))))) + +(define (%cars+ lists last-elt) ; (append! (map car lists) (list last-elt)) + (let recur ((lists lists)) + (if (pair? lists) (cons (caar lists) (recur (cdr lists))) (list last-elt)))) + +;;; LISTS is a (not very long) non-empty list of lists. +;;; Return two lists: the cars & the cdrs of the lists. +;;; However, if any of the lists is empty, just abort and return [() ()]. + +(define (%cars+cdrs lists) + (call-with-current-continuation + (lambda (abort) + (let recur ((lists lists)) + (if (pair? lists) + (receive (list other-lists) (car+cdr lists) + (if (null-list? list) (abort '() '()) ; LIST is empty -- bail out + (receive (a d) (car+cdr list) + (receive (cars cdrs) (recur other-lists) + (values (cons a cars) (cons d cdrs)))))) + (values '() '())))))) + +;;; Like %CARS+CDRS, but we pass in a final elt tacked onto the end of the +;;; cars list. What a hack. +(define (%cars+cdrs+ lists cars-final) + (call-with-current-continuation + (lambda (abort) + (let recur ((lists lists)) + (if (pair? lists) + (receive (list other-lists) (car+cdr lists) + (if (null-list? list) (abort '() '()) ; LIST is empty -- bail out + (receive (a d) (car+cdr list) + (receive (cars cdrs) (recur other-lists) + (values (cons a cars) (cons d cdrs)))))) + (values (list cars-final) '())))))) + +;;; Like %CARS+CDRS, but blow up if any list is empty. +(define (%cars+cdrs/no-test lists) + (let recur ((lists lists)) + (if (pair? lists) + (receive (list other-lists) (car+cdr lists) + (receive (a d) (car+cdr list) + (receive (cars cdrs) (recur other-lists) + (values (cons a cars) (cons d cdrs))))) + (values '() '())))) + + +;;; count +;;;;;;;;; +(define (count pred list1 . lists) + (check-arg procedure? pred count) + (if (pair? lists) + + ;; N-ary case + (let lp ((list1 list1) (lists lists) (i 0)) + (if (null-list? list1) i + (receive (as ds) (%cars+cdrs lists) + (if (null? as) i + (lp (cdr list1) ds + (if (apply pred (car list1) as) (+ i 1) i)))))) + + ;; Fast path + (let lp ((lis list1) (i 0)) + (if (null-list? lis) i + (lp (cdr lis) (if (pred (car lis)) (+ i 1) i)))))) + + +;;; fold/unfold +;;;;;;;;;;;;;;; + +(define (unfold-right p f g seed . maybe-tail) + (check-arg procedure? p unfold-right) + (check-arg procedure? f unfold-right) + (check-arg procedure? g unfold-right) + (let lp ((seed seed) (ans (:optional maybe-tail '()))) + (if (p seed) ans + (lp (g seed) + (cons (f seed) ans))))) + + +(define (unfold p f g seed . maybe-tail-gen) + (check-arg procedure? p unfold) + (check-arg procedure? f unfold) + (check-arg procedure? g unfold) + (if (pair? maybe-tail-gen) + + (let ((tail-gen (car maybe-tail-gen))) + (if (pair? (cdr maybe-tail-gen)) + (apply error "Too many arguments" unfold p f g seed maybe-tail-gen) + + (let recur ((seed seed)) + (if (p seed) (tail-gen seed) + (cons (f seed) (recur (g seed))))))) + + (let recur ((seed seed)) + (if (p seed) '() + (cons (f seed) (recur (g seed))))))) + + +(define (fold kons knil lis1 . lists) + (check-arg procedure? kons fold) + (if (pair? lists) + (let lp ((lists (cons lis1 lists)) (ans knil)) ; N-ary case + (receive (cars+ans cdrs) (%cars+cdrs+ lists ans) + (if (null? cars+ans) ans ; Done. + (lp cdrs (apply kons cars+ans))))) + + (let lp ((lis lis1) (ans knil)) ; Fast path + (if (null-list? lis) ans + (lp (cdr lis) (kons (car lis) ans)))))) + + +(define (fold-right kons knil lis1 . lists) + (check-arg procedure? kons fold-right) + (if (pair? lists) + (let recur ((lists (cons lis1 lists))) ; N-ary case + (let ((cdrs (%cdrs lists))) + (if (null? cdrs) knil + (apply kons (%cars+ lists (recur cdrs)))))) + + (let recur ((lis lis1)) ; Fast path + (if (null-list? lis) knil + (let ((head (car lis))) + (kons head (recur (cdr lis)))))))) + + +(define (pair-fold-right f zero lis1 . lists) + (check-arg procedure? f pair-fold-right) + (if (pair? lists) + (let recur ((lists (cons lis1 lists))) ; N-ary case + (let ((cdrs (%cdrs lists))) + (if (null? cdrs) zero + (apply f (append! lists (list (recur cdrs))))))) + + (let recur ((lis lis1)) ; Fast path + (if (null-list? lis) zero (f lis (recur (cdr lis))))))) + +(define (pair-fold f zero lis1 . lists) + (check-arg procedure? f pair-fold) + (if (pair? lists) + (let lp ((lists (cons lis1 lists)) (ans zero)) ; N-ary case + (let ((tails (%cdrs lists))) + (if (null? tails) ans + (lp tails (apply f (append! lists (list ans))))))) + + (let lp ((lis lis1) (ans zero)) + (if (null-list? lis) ans + (let ((tail (cdr lis))) ; Grab the cdr now, + (lp tail (f lis ans))))))) ; in case F SET-CDR!s LIS. + + +;;; REDUCE and REDUCE-RIGHT only use RIDENTITY in the empty-list case. +;;; These cannot meaningfully be n-ary. + +(define (reduce f ridentity lis) + (check-arg procedure? f reduce) + (if (null-list? lis) ridentity + (fold f (car lis) (cdr lis)))) + +(define (reduce-right f ridentity lis) + (check-arg procedure? f reduce-right) + (if (null-list? lis) ridentity + (let recur ((head (car lis)) (lis (cdr lis))) + (if (pair? lis) + (f head (recur (car lis) (cdr lis))) + head)))) + + + +;;; Mappers: append-map append-map! pair-for-each map! filter-map map-in-order +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(define (append-map f lis1 . lists) + (really-append-map append-map append f lis1 lists)) +(define (append-map! f lis1 . lists) + (really-append-map append-map! append! f lis1 lists)) + +(define (really-append-map who appender f lis1 lists) + (check-arg procedure? f who) + (if (pair? lists) + (receive (cars cdrs) (%cars+cdrs (cons lis1 lists)) + (if (null? cars) '() + (let recur ((cars cars) (cdrs cdrs)) + (let ((vals (apply f cars))) + (receive (cars2 cdrs2) (%cars+cdrs cdrs) + (if (null? cars2) vals + (appender vals (recur cars2 cdrs2)))))))) + + ;; Fast path + (if (null-list? lis1) '() + (let recur ((elt (car lis1)) (rest (cdr lis1))) + (let ((vals (f elt))) + (if (null-list? rest) vals + (appender vals (recur (car rest) (cdr rest))))))))) + + +(define (pair-for-each proc lis1 . lists) + (check-arg procedure? proc pair-for-each) + (if (pair? lists) + + (let lp ((lists (cons lis1 lists))) + (let ((tails (%cdrs lists))) + (if (pair? tails) + (begin (apply proc lists) + (lp tails))))) + + ;; Fast path. + (let lp ((lis lis1)) + (if (not (null-list? lis)) + (let ((tail (cdr lis))) ; Grab the cdr now, + (proc lis) ; in case PROC SET-CDR!s LIS. + (lp tail)))))) + +;;; We stop when LIS1 runs out, not when any list runs out. +(define (map! f lis1 . lists) + (check-arg procedure? f map!) + (if (pair? lists) + (let lp ((lis1 lis1) (lists lists)) + (if (not (null-list? lis1)) + (receive (heads tails) (%cars+cdrs/no-test lists) + (set-car! lis1 (apply f (car lis1) heads)) + (lp (cdr lis1) tails)))) + + ;; Fast path. + (pair-for-each (lambda (pair) (set-car! pair (f (car pair)))) lis1)) + lis1) + + +;;; Map F across L, and save up all the non-false results. +(define (filter-map f lis1 . lists) + (check-arg procedure? f filter-map) + (if (pair? lists) + (let recur ((lists (cons lis1 lists))) + (receive (cars cdrs) (%cars+cdrs lists) + (if (pair? cars) + (cond ((apply f cars) => (lambda (x) (cons x (recur cdrs)))) + (else (recur cdrs))) ; Tail call in this arm. + '()))) + + ;; Fast path. + (let recur ((lis lis1)) + (if (null-list? lis) lis + (let ((tail (recur (cdr lis)))) + (cond ((f (car lis)) => (lambda (x) (cons x tail))) + (else tail))))))) + + +;;; Map F across lists, guaranteeing to go left-to-right. +;;; NOTE: Some implementations of R5RS MAP are compliant with this spec; +;;; in which case this procedure may simply be defined as a synonym for MAP. + +(define (map-in-order f lis1 . lists) + (check-arg procedure? f map-in-order) + (if (pair? lists) + (let recur ((lists (cons lis1 lists))) + (receive (cars cdrs) (%cars+cdrs lists) + (if (pair? cars) + (let ((x (apply f cars))) ; Do head first, + (cons x (recur cdrs))) ; then tail. + '()))) + + ;; Fast path. + (let recur ((lis lis1)) + (if (null-list? lis) lis + (let ((tail (cdr lis)) + (x (f (car lis)))) ; Do head first, + (cons x (recur tail))))))) ; then tail. + + +;;; We extend MAP to handle arguments of unequal length. +(define map map-in-order) + + +;;; filter, remove, partition +;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;;; FILTER, REMOVE, PARTITION and their destructive counterparts do not +;;; disorder the elements of their argument. + +;; This FILTER shares the longest tail of L that has no deleted elements. +;; If Scheme had multi-continuation calls, they could be made more efficient. + +(define (filter pred lis) ; Sleazing with EQ? makes this + (check-arg procedure? pred filter) ; one faster. + (let recur ((lis lis)) + (if (null-list? lis) lis ; Use NOT-PAIR? to handle dotted lists. + (let ((head (car lis)) + (tail (cdr lis))) + (if (pred head) + (let ((new-tail (recur tail))) ; Replicate the RECUR call so + (if (eq? tail new-tail) lis + (cons head new-tail))) + (recur tail)))))) ; this one can be a tail call. + + +;;; Another version that shares longest tail. +;(define (filter pred lis) +; (receive (ans no-del?) +; ;; (recur l) returns L with (pred x) values filtered. +; ;; It also returns a flag NO-DEL? if the returned value +; ;; is EQ? to L, i.e. if it didn't have to delete anything. +; (let recur ((l l)) +; (if (null-list? l) (values l #t) +; (let ((x (car l)) +; (tl (cdr l))) +; (if (pred x) +; (receive (ans no-del?) (recur tl) +; (if no-del? +; (values l #t) +; (values (cons x ans) #f))) +; (receive (ans no-del?) (recur tl) ; Delete X. +; (values ans #f)))))) +; ans)) + + + +;(define (filter! pred lis) ; Things are much simpler +; (let recur ((lis lis)) ; if you are willing to +; (if (pair? lis) ; push N stack frames & do N +; (cond ((pred (car lis)) ; SET-CDR! writes, where N is +; (set-cdr! lis (recur (cdr lis))); the length of the answer. +; lis) +; (else (recur (cdr lis)))) +; lis))) + + +;;; This implementation of FILTER! +;;; - doesn't cons, and uses no stack; +;;; - is careful not to do redundant SET-CDR! writes, as writes to memory are +;;; usually expensive on modern machines, and can be extremely expensive on +;;; modern Schemes (e.g., ones that have generational GC's). +;;; It just zips down contiguous runs of in and out elts in LIS doing the +;;; minimal number of SET-CDR!s to splice the tail of one run of ins to the +;;; beginning of the next. + +(define (filter! pred lis) + (check-arg procedure? pred filter!) + (let lp ((ans lis)) + (cond ((null-list? ans) ans) ; Scan looking for + ((not (pred (car ans))) (lp (cdr ans))) ; first cons of result. + + ;; ANS is the eventual answer. + ;; SCAN-IN: (CDR PREV) = LIS and (CAR PREV) satisfies PRED. + ;; Scan over a contiguous segment of the list that + ;; satisfies PRED. + ;; SCAN-OUT: (CAR PREV) satisfies PRED. Scan over a contiguous + ;; segment of the list that *doesn't* satisfy PRED. + ;; When the segment ends, patch in a link from PREV + ;; to the start of the next good segment, and jump to + ;; SCAN-IN. + (else (letrec ((scan-in (lambda (prev lis) + (if (pair? lis) + (if (pred (car lis)) + (scan-in lis (cdr lis)) + (scan-out prev (cdr lis)))))) + (scan-out (lambda (prev lis) + (let lp ((lis lis)) + (if (pair? lis) + (if (pred (car lis)) + (begin (set-cdr! prev lis) + (scan-in lis (cdr lis))) + (lp (cdr lis))) + (set-cdr! prev lis)))))) + (scan-in ans (cdr ans)) + ans))))) + + + +;;; Answers share common tail with LIS where possible; +;;; the technique is slightly subtle. + +(define (partition pred lis) + (check-arg procedure? pred partition) + (let recur ((lis lis)) + (if (null-list? lis) (values lis lis) ; Use NOT-PAIR? to handle dotted lists. + (let ((elt (car lis)) + (tail (cdr lis))) + (receive (in out) (recur tail) + (if (pred elt) + (values (if (pair? out) (cons elt in) lis) out) + (values in (if (pair? in) (cons elt out) lis)))))))) + + + +;(define (partition! pred lis) ; Things are much simpler +; (let recur ((lis lis)) ; if you are willing to +; (if (null-list? lis) (values lis lis) ; push N stack frames & do N +; (let ((elt (car lis))) ; SET-CDR! writes, where N is +; (receive (in out) (recur (cdr lis)) ; the length of LIS. +; (cond ((pred elt) +; (set-cdr! lis in) +; (values lis out)) +; (else (set-cdr! lis out) +; (values in lis)))))))) + + +;;; This implementation of PARTITION! +;;; - doesn't cons, and uses no stack; +;;; - is careful not to do redundant SET-CDR! writes, as writes to memory are +;;; usually expensive on modern machines, and can be extremely expensive on +;;; modern Schemes (e.g., ones that have generational GC's). +;;; It just zips down contiguous runs of in and out elts in LIS doing the +;;; minimal number of SET-CDR!s to splice these runs together into the result +;;; lists. + +(define (partition! pred lis) + (check-arg procedure? pred partition!) + (if (null-list? lis) (values lis lis) + + ;; This pair of loops zips down contiguous in & out runs of the + ;; list, splicing the runs together. The invariants are + ;; SCAN-IN: (cdr in-prev) = LIS. + ;; SCAN-OUT: (cdr out-prev) = LIS. + (letrec ((scan-in (lambda (in-prev out-prev lis) + (let lp ((in-prev in-prev) (lis lis)) + (if (pair? lis) + (if (pred (car lis)) + (lp lis (cdr lis)) + (begin (set-cdr! out-prev lis) + (scan-out in-prev lis (cdr lis)))) + (set-cdr! out-prev lis))))) ; Done. + + (scan-out (lambda (in-prev out-prev lis) + (let lp ((out-prev out-prev) (lis lis)) + (if (pair? lis) + (if (pred (car lis)) + (begin (set-cdr! in-prev lis) + (scan-in lis out-prev (cdr lis))) + (lp lis (cdr lis))) + (set-cdr! in-prev lis)))))) ; Done. + + ;; Crank up the scan&splice loops. + (if (pred (car lis)) + ;; LIS begins in-list. Search for out-list's first pair. + (let lp ((prev-l lis) (l (cdr lis))) + (cond ((not (pair? l)) (values lis l)) + ((pred (car l)) (lp l (cdr l))) + (else (scan-out prev-l l (cdr l)) + (values lis l)))) ; Done. + + ;; LIS begins out-list. Search for in-list's first pair. + (let lp ((prev-l lis) (l (cdr lis))) + (cond ((not (pair? l)) (values l lis)) + ((pred (car l)) + (scan-in l prev-l (cdr l)) + (values l lis)) ; Done. + (else (lp l (cdr l))))))))) + + +;;; Inline us, please. +(define (remove pred l) (filter (lambda (x) (not (pred x))) l)) +(define (remove! pred l) (filter! (lambda (x) (not (pred x))) l)) + + + +;;; Here's the taxonomy for the DELETE/ASSOC/MEMBER functions. +;;; (I don't actually think these are the world's most important +;;; functions -- the procedural FILTER/REMOVE/FIND/FIND-TAIL variants +;;; are far more general.) +;;; +;;; Function Action +;;; --------------------------------------------------------------------------- +;;; remove pred lis Delete by general predicate +;;; delete x lis [=] Delete by element comparison +;;; +;;; find pred lis Search by general predicate +;;; find-tail pred lis Search by general predicate +;;; member x lis [=] Search by element comparison +;;; +;;; assoc key lis [=] Search alist by key comparison +;;; alist-delete key alist [=] Alist-delete by key comparison + +(define (delete x lis . maybe-=) + (let ((= (:optional maybe-= equal?))) + (filter (lambda (y) (not (= x y))) lis))) + +(define (delete! x lis . maybe-=) + (let ((= (:optional maybe-= equal?))) + (filter! (lambda (y) (not (= x y))) lis))) + +;;; Extended from R4RS to take an optional comparison argument. +(define (member x lis . maybe-=) + (let ((= (:optional maybe-= equal?))) + (find-tail (lambda (y) (= x y)) lis))) + +;;; R4RS, hence we don't bother to define. +;;; The MEMBER and then FIND-TAIL call should definitely +;;; be inlined for MEMQ & MEMV. +;(define (memq x lis) (member x lis eq?)) +;(define (memv x lis) (member x lis eqv?)) + + +;;; right-duplicate deletion +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;;; delete-duplicates delete-duplicates! +;;; +;;; Beware -- these are N^2 algorithms. To efficiently remove duplicates +;;; in long lists, sort the list to bring duplicates together, then use a +;;; linear-time algorithm to kill the dups. Or use an algorithm based on +;;; element-marking. The former gives you O(n lg n), the latter is linear. + +(define (delete-duplicates lis . maybe-=) + (let ((elt= (:optional maybe-= equal?))) + (check-arg procedure? elt= delete-duplicates) + (let recur ((lis lis)) + (if (null-list? lis) lis + (let* ((x (car lis)) + (tail (cdr lis)) + (new-tail (recur (delete x tail elt=)))) + (if (eq? tail new-tail) lis (cons x new-tail))))))) + +(define (delete-duplicates! lis maybe-=) + (let ((elt= (:optional maybe-= equal?))) + (check-arg procedure? elt= delete-duplicates!) + (let recur ((lis lis)) + (if (null-list? lis) lis + (let* ((x (car lis)) + (tail (cdr lis)) + (new-tail (recur (delete! x tail elt=)))) + (if (eq? tail new-tail) lis (cons x new-tail))))))) + + +;;; alist stuff +;;;;;;;;;;;;;;; + +;;; Extended from R4RS to take an optional comparison argument. +(define (assoc x lis . maybe-=) + (let ((= (:optional maybe-= equal?))) + (find (lambda (entry) (= x (car entry))) lis))) + +(define (alist-cons key datum alist) (cons (cons key datum) alist)) + +(define (alist-copy alist) + (map (lambda (elt) (cons (car elt) (cdr elt))) + alist)) + +(define (alist-delete key alist . maybe-=) + (let ((= (:optional maybe-= equal?))) + (filter (lambda (elt) (not (= key (car elt)))) alist))) + +(define (alist-delete! key alist . maybe-=) + (let ((= (:optional maybe-= equal?))) + (filter! (lambda (elt) (not (= key (car elt)))) alist))) + + +;;; find find-tail take-while drop-while span break any every list-index +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(define (find pred list) + (cond ((find-tail pred list) => car) + (else #f))) + +(define (find-tail pred list) + (check-arg procedure? pred find-tail) + (let lp ((list list)) + (and (not (null-list? list)) + (if (pred (car list)) list + (lp (cdr list)))))) + +(define (take-while pred lis) + (check-arg procedure? pred take-while) + (let recur ((lis lis)) + (if (null-list? lis) '() + (let ((x (car lis))) + (if (pred x) + (cons x (recur (cdr lis))) + '()))))) + +(define (drop-while pred lis) + (check-arg procedure? pred drop-while) + (let lp ((lis lis)) + (if (null-list? lis) '() + (if (pred (car lis)) + (lp (cdr lis)) + lis)))) + +(define (take-while! pred lis) + (check-arg procedure? pred take-while!) + (if (or (null-list? lis) (not (pred (car lis)))) '() + (begin (let lp ((prev lis) (rest (cdr lis))) + (if (pair? rest) + (let ((x (car rest))) + (if (pred x) (lp rest (cdr rest)) + (set-cdr! prev '()))))) + lis))) + +(define (span pred lis) + (check-arg procedure? pred span) + (let recur ((lis lis)) + (if (null-list? lis) (values '() '()) + (let ((x (car lis))) + (if (pred x) + (receive (prefix suffix) (recur (cdr lis)) + (values (cons x prefix) suffix)) + (values '() lis)))))) + +(define (span! pred lis) + (check-arg procedure? pred span!) + (if (or (null-list? lis) (not (pred (car lis)))) (values '() lis) + (let ((suffix (let lp ((prev lis) (rest (cdr lis))) + (if (null-list? rest) rest + (let ((x (car rest))) + (if (pred x) (lp rest (cdr rest)) + (begin (set-cdr! prev '()) + rest))))))) + (values lis suffix)))) + + +(define (break pred lis) (span (lambda (x) (not (pred x))) lis)) +(define (break! pred lis) (span! (lambda (x) (not (pred x))) lis)) + +(define (any pred lis1 . lists) + (check-arg procedure? pred any) + (if (pair? lists) + + ;; N-ary case + (receive (heads tails) (%cars+cdrs (cons lis1 lists)) + (and (pair? heads) + (let lp ((heads heads) (tails tails)) + (receive (next-heads next-tails) (%cars+cdrs tails) + (if (pair? next-heads) + (or (apply pred heads) (lp next-heads next-tails)) + (apply pred heads)))))) ; Last PRED app is tail call. + + ;; Fast path + (and (not (null-list? lis1)) + (let lp ((head (car lis1)) (tail (cdr lis1))) + (if (null-list? tail) + (pred head) ; Last PRED app is tail call. + (or (pred head) (lp (car tail) (cdr tail)))))))) + + +;(define (every pred list) ; Simple definition. +; (let lp ((list list)) ; Doesn't return the last PRED value. +; (or (not (pair? list)) +; (and (pred (car list)) +; (lp (cdr list)))))) + +(define (every pred lis1 . lists) + (check-arg procedure? pred every) + (if (pair? lists) + + ;; N-ary case + (receive (heads tails) (%cars+cdrs (cons lis1 lists)) + (or (not (pair? heads)) + (let lp ((heads heads) (tails tails)) + (receive (next-heads next-tails) (%cars+cdrs tails) + (if (pair? next-heads) + (and (apply pred heads) (lp next-heads next-tails)) + (apply pred heads)))))) ; Last PRED app is tail call. + + ;; Fast path + (or (null-list? lis1) + (let lp ((head (car lis1)) (tail (cdr lis1))) + (if (null-list? tail) + (pred head) ; Last PRED app is tail call. + (and (pred head) (lp (car tail) (cdr tail)))))))) + +(define (list-index pred lis1 . lists) + (check-arg procedure? pred list-index) + (if (pair? lists) + + ;; N-ary case + (let lp ((lists (cons lis1 lists)) (n 0)) + (receive (heads tails) (%cars+cdrs lists) + (and (pair? heads) + (if (apply pred heads) n + (lp tails (+ n 1)))))) + + ;; Fast path + (let lp ((lis lis1) (n 0)) + (and (not (null-list? lis)) + (if (pred (car lis)) n (lp (cdr lis) (+ n 1))))))) + +;;; Reverse +;;;;;;;;;;; + +;R4RS, so not defined here. +;(define (reverse lis) (fold cons '() lis)) + +;(define (reverse! lis) +; (pair-fold (lambda (pair tail) (set-cdr! pair tail) pair) '() lis)) + +(define (reverse! lis) + (let lp ((lis lis) (ans '())) + (if (null-list? lis) ans + (let ((tail (cdr lis))) + (set-cdr! lis ans) + (lp tail lis))))) + +;;; Lists-as-sets +;;;;;;;;;;;;;;;;; + +;;; 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. +;;; - It tries to avoid linear-time scans in special cases where constant-time +;;; computations can be performed. +;;; - It relies on similar properties from the other list-lib procs it calls. +;;; For example, it uses the fact that the implementations of MEMBER and +;;; FILTER in this source code share longest common tails between args +;;; and results to get structure sharing in the lset procedures. + +(define (%lset2<= = lis1 lis2) (every (lambda (x) (member x lis2 =)) lis1)) + +(define (lset<= = . lists) + (check-arg procedure? = lset<=) + (or (not (pair? lists)) ; 0-ary case + (let lp ((s1 (car lists)) (rest (cdr lists))) + (or (not (pair? rest)) + (let ((s2 (car rest)) (rest (cdr rest))) + (and (or (eq? s2 s1) ; Fast path + (%lset2<= = s1 s2)) ; Real test + (lp s2 rest))))))) + +(define (lset= = . lists) + (check-arg procedure? = lset=) + (or (not (pair? lists)) ; 0-ary case + (let lp ((s1 (car lists)) (rest (cdr lists))) + (or (not (pair? rest)) + (let ((s2 (car rest)) + (rest (cdr rest))) + (and (or (eq? s1 s2) ; Fast path + (and (%lset2<= = s1 s2) (%lset2<= = s2 s1))) ; Real test + (lp s2 rest))))))) + + +(define (lset-adjoin = lis . elts) + (check-arg procedure? = lset-adjoin) + (fold (lambda (elt ans) (if (member elt ans =) ans (cons elt ans))) + lis elts)) + + +(define (lset-union = . lists) + (check-arg procedure? = lset-union) + (reduce (lambda (lis ans) ; Compute ANS + LIS. + (cond ((null? lis) ans) ; Don't copy any lists + ((null? ans) lis) ; if we don't have to. + ((eq? lis ans) ans) + (else + (fold (lambda (elt ans) (if (any (lambda (x) (= x elt)) ans) + ans + (cons elt ans))) + ans lis)))) + '() lists)) + +(define (lset-union! = . lists) + (check-arg procedure? = lset-union!) + (reduce (lambda (lis ans) ; Splice new elts of LIS onto the front of ANS. + (cond ((null? lis) ans) ; Don't copy any lists + ((null? ans) lis) ; if we don't have to. + ((eq? lis ans) ans) + (else + (pair-fold (lambda (pair ans) + (let ((elt (car pair))) + (if (any (lambda (x) (= x elt)) ans) + ans + (begin (set-cdr! pair ans) pair)))) + ans lis)))) + '() lists)) + + +(define (lset-intersection = lis1 . lists) + (check-arg procedure? = lset-intersection) + (let ((lists (delete lis1 lists eq?))) ; Throw out any LIS1 vals. + (cond ((any null-list? lists) '()) ; Short cut + ((null? lists) lis1) ; Short cut + (else (filter (lambda (x) + (every (lambda (lis) (member x lis =)) lists)) + lis1))))) + +(define (lset-intersection! = lis1 . lists) + (check-arg procedure? = lset-intersection!) + (let ((lists (delete lis1 lists eq?))) ; Throw out any LIS1 vals. + (cond ((any null-list? lists) '()) ; Short cut + ((null? lists) lis1) ; Short cut + (else (filter! (lambda (x) + (every (lambda (lis) (member x lis =)) lists)) + lis1))))) + + +(define (lset-difference = lis1 . lists) + (check-arg procedure? = lset-difference) + (let ((lists (filter pair? lists))) ; Throw out empty lists. + (cond ((null? lists) lis1) ; Short cut + ((memq lis1 lists) '()) ; Short cut + (else (filter (lambda (x) + (every (lambda (lis) (not (member x lis =))) + lists)) + lis1))))) + +(define (lset-difference! = lis1 . lists) + (check-arg procedure? = lset-difference!) + (let ((lists (filter pair? lists))) ; Throw out empty lists. + (cond ((null? lists) lis1) ; Short cut + ((memq lis1 lists) '()) ; Short cut + (else (filter! (lambda (x) + (every (lambda (lis) (not (member x lis =))) + lists)) + lis1))))) + + +(define (lset-xor = . lists) + (check-arg procedure? = lset-xor) + (reduce (lambda (b a) ; Compute A xor B: + ;; Note that this code relies on the constant-time + ;; short-cuts provided by LSET-DIFF+INTERSECTION, + ;; LSET-DIFFERENCE & APPEND to provide constant-time short + ;; cuts for the cases A = (), B = (), and A eq? B. It takes + ;; a careful case analysis to see it, but it's carefully + ;; built in. + + ;; Compute a-b and a^b, then compute b-(a^b) and + ;; cons it onto the front of a-b. + (receive (a-b a-int-b) (lset-diff+intersection = a b) + (cond ((null? a-b) (lset-difference b a =)) + ((null? a-int-b) (append b a)) + (else (fold (lambda (xb ans) + (if (member xb a-int-b =) ans (cons xb ans))) + a-b + b))))) + '() lists)) + + +(define (lset-xor! = . lists) + (check-arg procedure? = lset-xor!) + (reduce (lambda (b a) ; Compute A xor B: + ;; Note that this code relies on the constant-time + ;; short-cuts provided by LSET-DIFF+INTERSECTION, + ;; LSET-DIFFERENCE & APPEND to provide constant-time short + ;; cuts for the cases A = (), B = (), and A eq? B. It takes + ;; a careful case analysis to see it, but it's carefully + ;; built in. + + ;; Compute a-b and a^b, then compute b-(a^b) and + ;; cons it onto the front of a-b. + (receive (a-b a-int-b) (lset-diff+intersection! = a b) + (cond ((null? a-b) (lset-difference! b a =)) + ((null? a-int-b) (append! b a)) + (else (pair-fold (lambda (b-pair ans) + (if (member (car b-pair) a-int-b =) ans + (begin (set-cdr! b-pair ans) b-pair))) + a-b + b))))) + '() lists)) + + +(define (lset-diff+intersection = lis1 . lists) + (check-arg procedure? = lset-diff+intersection) + (cond ((every null-list? lists) (values lis1 '())) ; Short cut + ((memq lis1 lists) (values '() lis1)) ; Short cut + (else (partition (lambda (elt) + (not (any (lambda (lis) (member elt lis =)) + lists))) + lis1)))) + +(define (lset-diff+intersection! = lis1 . lists) + (check-arg procedure? = lset-diff+intersection!) + (cond ((every null-list? lists) (values lis1 '())) ; Short cut + ((memq lis1 lists) (values '() lis1)) ; Short cut + (else (partition! (lambda (elt) + (not (any (lambda (lis) (member elt lis =)) + lists))) + lis1))))
