diff --git a/chibi/match.sld b/chibi/match.sld new file mode 100644 index 0000000..36a652b --- /dev/null +++ b/chibi/match.sld @@ -0,0 +1,7 @@ + +(define-library (chibi match) + (export match match-lambda match-lambda* match-let match-letrec match-let*) + (cond-expand + (chibi (import (chibi))) + (else (import (scheme base)))) + (include "match/match.scm")) diff --git a/chibi/match/match.scm b/chibi/match/match.scm new file mode 100644 index 0000000..4a5d038 --- /dev/null +++ b/chibi/match/match.scm @@ -0,0 +1,972 @@ +;;;; match.scm -- portable hygienic pattern matcher -*- coding: utf-8 -*- +;; +;; This code is written by Alex Shinn and placed in the +;; Public Domain. All warranties are disclaimed. + +;;> \example-import[(srfi 9)] + +;;> A portable hygienic pattern matcher. + +;;> This is a full superset of the popular \hyperlink[ +;;> "http://www.cs.indiana.edu/scheme-repository/code.match.html"]{match} +;;> package by Andrew Wright, written in fully portable \scheme{syntax-rules} +;;> and thus preserving hygiene. + +;;> The most notable extensions are the ability to use \emph{non-linear} +;;> patterns - patterns in which the same identifier occurs multiple +;;> times, tail patterns after ellipsis, and the experimental tree patterns. + +;;> \section{Patterns} + +;;> Patterns are written to look like the printed representation of +;;> the objects they match. The basic usage is + +;;> \scheme{(match expr (pat body ...) ...)} + +;;> where the result of \var{expr} is matched against each pattern in +;;> turn, and the corresponding body is evaluated for the first to +;;> succeed. Thus, a list of three elements matches a list of three +;;> elements. + +;;> \example{(let ((ls (list 1 2 3))) (match ls ((1 2 3) #t)))} + +;;> If no patterns match an error is signalled. + +;;> Identifiers will match anything, and make the corresponding +;;> binding available in the body. + +;;> \example{(match (list 1 2 3) ((a b c) b))} + +;;> If the same identifier occurs multiple times, the first instance +;;> will match anything, but subsequent instances must match a value +;;> which is \scheme{equal?} to the first. + +;;> \example{(match (list 1 2 1) ((a a b) 1) ((a b a) 2))} + +;;> The special identifier \scheme{_} matches anything, no matter how +;;> many times it is used, and does not bind the result in the body. + +;;> \example{(match (list 1 2 1) ((_ _ b) 1) ((a b a) 2))} + +;;> To match a literal identifier (or list or any other literal), use +;;> \scheme{quote}. + +;;> \example{(match 'a ('b 1) ('a 2))} + +;;> Analogous to its normal usage in scheme, \scheme{quasiquote} can +;;> be used to quote a mostly literally matching object with selected +;;> parts unquoted. + +;;> \example|{(match (list 1 2 3) (`(1 ,b ,c) (list b c)))}| + +;;> Often you want to match any number of a repeated pattern. Inside +;;> a list pattern you can append \scheme{...} after an element to +;;> match zero or more of that pattern (like a regexp Kleene star). + +;;> \example{(match (list 1 2) ((1 2 3 ...) #t))} +;;> \example{(match (list 1 2 3) ((1 2 3 ...) #t))} +;;> \example{(match (list 1 2 3 3 3) ((1 2 3 ...) #t))} + +;;> Pattern variables matched inside the repeated pattern are bound to +;;> a list of each matching instance in the body. + +;;> \example{(match (list 1 2) ((a b c ...) c))} +;;> \example{(match (list 1 2 3) ((a b c ...) c))} +;;> \example{(match (list 1 2 3 4 5) ((a b c ...) c))} + +;;> More than one \scheme{...} may not be used in the same list, since +;;> this would require exponential backtracking in the general case. +;;> However, \scheme{...} need not be the final element in the list, +;;> and may be succeeded by a fixed number of patterns. + +;;> \example{(match (list 1 2 3 4) ((a b c ... d e) c))} +;;> \example{(match (list 1 2 3 4 5) ((a b c ... d e) c))} +;;> \example{(match (list 1 2 3 4 5 6 7) ((a b c ... d e) c))} + +;;> \scheme{___} is provided as an alias for \scheme{...} when it is +;;> inconvenient to use the ellipsis (as in a syntax-rules template). + +;;> The \scheme{..1} syntax is exactly like the \scheme{...} except +;;> that it matches one or more repetitions (like a regexp "+"). + +;;> \example{(match (list 1 2) ((a b c ..1) c))} +;;> \example{(match (list 1 2 3) ((a b c ..1) c))} + +;;> The boolean operators \scheme{and}, \scheme{or} and \scheme{not} +;;> can be used to group and negate patterns analogously to their +;;> Scheme counterparts. + +;;> The \scheme{and} operator ensures that all subpatterns match. +;;> This operator is often used with the idiom \scheme{(and x pat)} to +;;> bind \var{x} to the entire value that matches \var{pat} +;;> (c.f. "as-patterns" in ML or Haskell). Another common use is in +;;> conjunction with \scheme{not} patterns to match a general case +;;> with certain exceptions. + +;;> \example{(match 1 ((and) #t))} +;;> \example{(match 1 ((and x) x))} +;;> \example{(match 1 ((and x 1) x))} + +;;> The \scheme{or} operator ensures that at least one subpattern +;;> matches. If the same identifier occurs in different subpatterns, +;;> it is matched independently. All identifiers from all subpatterns +;;> are bound if the \scheme{or} operator matches, but the binding is +;;> only defined for identifiers from the subpattern which matched. + +;;> \example{(match 1 ((or) #t) (else #f))} +;;> \example{(match 1 ((or x) x))} +;;> \example{(match 1 ((or x 2) x))} + +;;> The \scheme{not} operator succeeds if the given pattern doesn't +;;> match. None of the identifiers used are available in the body. + +;;> \example{(match 1 ((not 2) #t))} + +;;> The more general operator \scheme{?} can be used to provide a +;;> predicate. The usage is \scheme{(? predicate pat ...)} where +;;> \var{predicate} is a Scheme expression evaluating to a predicate +;;> called on the value to match, and any optional patterns after the +;;> predicate are then matched as in an \scheme{and} pattern. + +;;> \example{(match 1 ((? odd? x) x))} + +;;> The field operator \scheme{=} is used to extract an arbitrary +;;> field and match against it. It is useful for more complex or +;;> conditional destructuring that can't be more directly expressed in +;;> the pattern syntax. The usage is \scheme{(= field pat)}, where +;;> \var{field} can be any expression, and should result in a +;;> procedure of one argument, which is applied to the value to match +;;> to generate a new value to match against \var{pat}. + +;;> Thus the pattern \scheme{(and (= car x) (= cdr y))} is equivalent +;;> to \scheme{(x . y)}, except it will result in an immediate error +;;> if the value isn't a pair. + +;;> \example{(match '(1 . 2) ((= car x) x))} +;;> \example{(match 4 ((= square x) x))} + +;;> The record operator \scheme{$} is used as a concise way to match +;;> records defined by SRFI-9 (or SRFI-99). The usage is +;;> \scheme{($ rtd field ...)}, where \var{rtd} should be the record +;;> type descriptor specified as the first argument to +;;> \scheme{define-record-type}, and each \var{field} is a subpattern +;;> matched against the fields of the record in order. Not all fields +;;> must be present. + +;;> \example{ +;;> (let () +;;> (define-record-type employee +;;> (make-employee name title) +;;> employee? +;;> (name get-name) +;;> (title get-title)) +;;> (match (make-employee "Bob" "Doctor") +;;> (($ employee n t) (list t n)))) +;;> } + +;;> For records with more fields it can be helpful to match them by +;;> name rather than position. For this you can use the \scheme{@} +;;> operator, originally a Gauche extension: + +;;> \example{ +;;> (let () +;;> (define-record-type employee +;;> (make-employee name title) +;;> employee? +;;> (name get-name) +;;> (title get-title)) +;;> (match (make-employee "Bob" "Doctor") +;;> ((@ employee (title t) (name n)) (list t n)))) +;;> } + +;;> The \scheme{set!} and \scheme{get!} operators are used to bind an +;;> identifier to the setter and getter of a field, respectively. The +;;> setter is a procedure of one argument, which mutates the field to +;;> that argument. The getter is a procedure of no arguments which +;;> returns the current value of the field. + +;;> \example{(let ((x (cons 1 2))) (match x ((1 . (set! s)) (s 3) x)))} +;;> \example{(match '(1 . 2) ((1 . (get! g)) (g)))} + +;;> The new operator \scheme{***} can be used to search a tree for +;;> subpatterns. A pattern of the form \scheme{(x *** y)} represents +;;> the subpattern \var{y} located somewhere in a tree where the path +;;> from the current object to \var{y} can be seen as a list of the +;;> form \scheme{(x ...)}. \var{y} can immediately match the current +;;> object in which case the path is the empty list. In a sense it's +;;> a 2-dimensional version of the \scheme{...} pattern. + +;;> As a common case the pattern \scheme{(_ *** y)} can be used to +;;> search for \var{y} anywhere in a tree, regardless of the path +;;> used. + +;;> \example{(match '(a (a (a b))) ((x *** 'b) x))} +;;> \example{(match '(a (b) (c (d e) (f g))) ((x *** 'g) x))} + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Notes + +;; The implementation is a simple generative pattern matcher - each +;; pattern is expanded into the required tests, calling a failure +;; continuation if the tests fail. This makes the logic easy to +;; follow and extend, but produces sub-optimal code in cases where you +;; have many similar clauses due to repeating the same tests. +;; Nonetheless a smart compiler should be able to remove the redundant +;; tests. For MATCH-LET and DESTRUCTURING-BIND type uses there is no +;; performance hit. + +;; The original version was written on 2006/11/29 and described in the +;; following Usenet post: +;; http://groups.google.com/group/comp.lang.scheme/msg/0941234de7112ffd +;; and is still available at +;; http://synthcode.com/scheme/match-simple.scm +;; It's just 80 lines for the core MATCH, and an extra 40 lines for +;; MATCH-LET, MATCH-LAMBDA and other syntactic sugar. +;; +;; A variant of this file which uses COND-EXPAND in a few places for +;; performance can be found at +;; http://synthcode.com/scheme/match-cond-expand.scm +;; +;; 2015/05/09 - fixing bug in var extraction of quasiquote patterns +;; 2014/11/24 - adding Gauche's `@' pattern for named record field matching +;; 2012/12/26 - wrapping match-let&co body in lexical closure +;; 2012/11/28 - fixing typo s/vetor/vector in largely unused set! code +;; 2012/05/23 - fixing combinatorial explosion of code in certain or patterns +;; 2011/09/25 - fixing bug when directly matching an identifier repeated in +;; the pattern (thanks to Stefan Israelsson Tampe) +;; 2011/01/27 - fixing bug when matching tail patterns against improper lists +;; 2010/09/26 - adding `..1' patterns (thanks to Ludovic Courtès) +;; 2010/09/07 - fixing identifier extraction in some `...' and `***' patterns +;; 2009/11/25 - adding `***' tree search patterns +;; 2008/03/20 - fixing bug where (a ...) matched non-lists +;; 2008/03/15 - removing redundant check in vector patterns +;; 2008/03/06 - you can use `...' portably now (thanks to Taylor Campbell) +;; 2007/09/04 - fixing quasiquote patterns +;; 2007/07/21 - allowing ellipsis patterns in non-final list positions +;; 2007/04/10 - fixing potential hygiene issue in match-check-ellipsis +;; (thanks to Taylor Campbell) +;; 2007/04/08 - clean up, commenting +;; 2006/12/24 - bugfixes +;; 2006/12/01 - non-linear patterns, shared variables in OR, get!/set! + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; force compile-time syntax errors with useful messages + +(define-syntax match-syntax-error + (syntax-rules () + ((_) (match-syntax-error "invalid match-syntax-error usage")))) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;;> \section{Syntax} + +;;> \macro{(match expr (pattern . body) ...)\br{} +;;> (match expr (pattern (=> failure) . body) ...)} + +;;> The result of \var{expr} is matched against each \var{pattern} in +;;> turn, according to the pattern rules described in the previous +;;> section, until the the first \var{pattern} matches. When a match is +;;> found, the corresponding \var{body}s are evaluated in order, +;;> and the result of the last expression is returned as the result +;;> of the entire \scheme{match}. If a \var{failure} is provided, +;;> then it is bound to a procedure of no arguments which continues, +;;> processing at the next \var{pattern}. If no \var{pattern} matches, +;;> an error is signalled. + +;; The basic interface. MATCH just performs some basic syntax +;; validation, binds the match expression to a temporary variable `v', +;; and passes it on to MATCH-NEXT. It's a constant throughout the +;; code below that the binding `v' is a direct variable reference, not +;; an expression. + +(define-syntax match + (syntax-rules () + ((match) + (match-syntax-error "missing match expression")) + ((match atom) + (match-syntax-error "no match clauses")) + ((match (app ...) (pat . body) ...) + (let ((v (app ...))) + (match-next v ((app ...) (set! (app ...))) (pat . body) ...))) + ((match #(vec ...) (pat . body) ...) + (let ((v #(vec ...))) + (match-next v (v (set! v)) (pat . body) ...))) + ((match atom (pat . body) ...) + (let ((v atom)) + (match-next v (atom (set! atom)) (pat . body) ...))) + )) + +;; MATCH-NEXT passes each clause to MATCH-ONE in turn with its failure +;; thunk, which is expanded by recursing MATCH-NEXT on the remaining +;; clauses. `g+s' is a list of two elements, the get! and set! +;; expressions respectively. + +(define-syntax match-next + (syntax-rules (=>) + ;; no more clauses, the match failed + ((match-next v g+s) + (error 'match "no matching pattern")) + ;; named failure continuation + ((match-next v g+s (pat (=> failure) . body) . rest) + (let ((failure (lambda () (match-next v g+s . rest)))) + ;; match-one analyzes the pattern for us + (match-one v pat g+s (match-drop-ids (begin . body)) (failure) ()))) + ;; anonymous failure continuation, give it a dummy name + ((match-next v g+s (pat . body) . rest) + (match-next v g+s (pat (=> failure) . body) . rest)))) + +;; MATCH-ONE first checks for ellipsis patterns, otherwise passes on to +;; MATCH-TWO. + +(define-syntax match-one + (syntax-rules () + ;; If it's a list of two or more values, check to see if the + ;; second one is an ellipsis and handle accordingly, otherwise go + ;; to MATCH-TWO. + ((match-one v (p q . r) g+s sk fk i) + (match-check-ellipsis + q + (match-extract-vars p (match-gen-ellipsis v p r g+s sk fk i) i ()) + (match-two v (p q . r) g+s sk fk i))) + ;; Go directly to MATCH-TWO. + ((match-one . x) + (match-two . x)))) + +;; This is the guts of the pattern matcher. We are passed a lot of +;; information in the form: +;; +;; (match-two var pattern getter setter success-k fail-k (ids ...)) +;; +;; usually abbreviated +;; +;; (match-two v p g+s sk fk i) +;; +;; where VAR is the symbol name of the current variable we are +;; matching, PATTERN is the current pattern, getter and setter are the +;; corresponding accessors (e.g. CAR and SET-CAR! of the pair holding +;; VAR), SUCCESS-K is the success continuation, FAIL-K is the failure +;; continuation (which is just a thunk call and is thus safe to expand +;; multiple times) and IDS are the list of identifiers bound in the +;; pattern so far. + +(define-syntax match-two + (syntax-rules (_ ___ ..1 *** quote quasiquote ? $ struct @ object = and or not set! get!) + ((match-two v () g+s (sk ...) fk i) + (if (null? v) (sk ... i) fk)) + ((match-two v (quote p) g+s (sk ...) fk i) + (if (equal? v 'p) (sk ... i) fk)) + ((match-two v (quasiquote p) . x) + (match-quasiquote v p . x)) + ((match-two v (and) g+s (sk ...) fk i) (sk ... i)) + ((match-two v (and p q ...) g+s sk fk i) + (match-one v p g+s (match-one v (and q ...) g+s sk fk) fk i)) + ((match-two v (or) g+s sk fk i) fk) + ((match-two v (or p) . x) + (match-one v p . x)) + ((match-two v (or p ...) g+s sk fk i) + (match-extract-vars (or p ...) (match-gen-or v (p ...) g+s sk fk i) i ())) + ((match-two v (not p) g+s (sk ...) fk i) + (match-one v p g+s (match-drop-ids fk) (sk ... i) i)) + ((match-two v (get! getter) (g s) (sk ...) fk i) + (let ((getter (lambda () g))) (sk ... i))) + ((match-two v (set! setter) (g (s ...)) (sk ...) fk i) + (let ((setter (lambda (x) (s ... x)))) (sk ... i))) + ((match-two v (? pred . p) g+s sk fk i) + (if (pred v) (match-one v (and . p) g+s sk fk i) fk)) + ((match-two v (= proc p) . x) + (let ((w (proc v))) (match-one w p . x))) + ((match-two v (p ___ . r) g+s sk fk i) + (match-extract-vars p (match-gen-ellipsis v p r g+s sk fk i) i ())) + ((match-two v (p) g+s sk fk i) + (if (and (pair? v) (null? (cdr v))) + (let ((w (car v))) + (match-one w p ((car v) (set-car! v)) sk fk i)) + fk)) + ((match-two v (p *** q) g+s sk fk i) + (match-extract-vars p (match-gen-search v p q g+s sk fk i) i ())) + ((match-two v (p *** . q) g+s sk fk i) + (match-syntax-error "invalid use of ***" (p *** . q))) + ((match-two v (p ..1) g+s sk fk i) + (if (pair? v) + (match-one v (p ___) g+s sk fk i) + fk)) + ((match-two v ($ rec p ...) g+s sk fk i) + (if (is-a? v rec) + (match-record-refs v rec 0 (p ...) g+s sk fk i) + fk)) + ((match-two v (struct rec p ...) g+s sk fk i) + (if (is-a? v rec) + (match-record-refs v rec 0 (p ...) g+s sk fk i) + fk)) + ((match-two v (@ rec p ...) g+s sk fk i) + (if (is-a? v rec) + (match-record-named-refs v rec (p ...) g+s sk fk i) + fk)) + ((match-two v (object rec p ...) g+s sk fk i) + (if (is-a? v rec) + (match-record-named-refs v rec (p ...) g+s sk fk i) + fk)) + ((match-two v (p . q) g+s sk fk i) + (if (pair? v) + (let ((w (car v)) (x (cdr v))) + (match-one w p ((car v) (set-car! v)) + (match-one x q ((cdr v) (set-cdr! v)) sk fk) + fk + i)) + fk)) + ((match-two v #(p ...) g+s . x) + (match-vector v 0 () (p ...) . x)) + ((match-two v _ g+s (sk ...) fk i) (sk ... i)) + ;; Not a pair or vector or special literal, test to see if it's a + ;; new symbol, in which case we just bind it, or if it's an + ;; already bound symbol or some other literal, in which case we + ;; compare it with EQUAL?. + ((match-two v x g+s (sk ...) fk (id ...)) + (let-syntax + ((new-sym? + (syntax-rules (id ...) + ((new-sym? x sk2 fk2) sk2) + ((new-sym? y sk2 fk2) fk2)))) + (new-sym? random-sym-to-match + (let ((x v)) (sk ... (id ... x))) + (if (equal? v x) (sk ... (id ...)) fk)))) + )) + +;; QUASIQUOTE patterns + +(define-syntax match-quasiquote + (syntax-rules (unquote unquote-splicing quasiquote) + ((_ v (unquote p) g+s sk fk i) + (match-one v p g+s sk fk i)) + ((_ v ((unquote-splicing p) . rest) g+s sk fk i) + (if (pair? v) + (match-one v + (p . tmp) + (match-quasiquote tmp rest g+s sk fk) + fk + i) + fk)) + ((_ v (quasiquote p) g+s sk fk i . depth) + (match-quasiquote v p g+s sk fk i #f . depth)) + ((_ v (unquote p) g+s sk fk i x . depth) + (match-quasiquote v p g+s sk fk i . depth)) + ((_ v (unquote-splicing p) g+s sk fk i x . depth) + (match-quasiquote v p g+s sk fk i . depth)) + ((_ v (p . q) g+s sk fk i . depth) + (if (pair? v) + (let ((w (car v)) (x (cdr v))) + (match-quasiquote + w p g+s + (match-quasiquote-step x q g+s sk fk depth) + fk i . depth)) + fk)) + ((_ v #(elt ...) g+s sk fk i . depth) + (if (vector? v) + (let ((ls (vector->list v))) + (match-quasiquote ls (elt ...) g+s sk fk i . depth)) + fk)) + ((_ v x g+s sk fk i . depth) + (match-one v 'x g+s sk fk i)))) + +(define-syntax match-quasiquote-step + (syntax-rules () + ((match-quasiquote-step x q g+s sk fk depth i) + (match-quasiquote x q g+s sk fk i . depth)))) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Utilities + +;; Takes two values and just expands into the first. +(define-syntax match-drop-ids + (syntax-rules () + ((_ expr ids ...) expr))) + +(define-syntax match-tuck-ids + (syntax-rules () + ((_ (letish args (expr ...)) ids ...) + (letish args (expr ... ids ...))))) + +(define-syntax match-drop-first-arg + (syntax-rules () + ((_ arg expr) expr))) + +;; To expand an OR group we try each clause in succession, passing the +;; first that succeeds to the success continuation. On failure for +;; any clause, we just try the next clause, finally resorting to the +;; failure continuation fk if all clauses fail. The only trick is +;; that we want to unify the identifiers, so that the success +;; continuation can refer to a variable from any of the OR clauses. + +(define-syntax match-gen-or + (syntax-rules () + ((_ v p g+s (sk ...) fk (i ...) ((id id-ls) ...)) + (let ((sk2 (lambda (id ...) (sk ... (i ... id ...))))) + (match-gen-or-step v p g+s (match-drop-ids (sk2 id ...)) fk (i ...)))))) + +(define-syntax match-gen-or-step + (syntax-rules () + ((_ v () g+s sk fk . x) + ;; no OR clauses, call the failure continuation + fk) + ((_ v (p) . x) + ;; last (or only) OR clause, just expand normally + (match-one v p . x)) + ((_ v (p . q) g+s sk fk i) + ;; match one and try the remaining on failure + (let ((fk2 (lambda () (match-gen-or-step v q g+s sk fk i)))) + (match-one v p g+s sk (fk2) i))) + )) + +;; We match a pattern (p ...) by matching the pattern p in a loop on +;; each element of the variable, accumulating the bound ids into lists. + +;; Look at the body of the simple case - it's just a named let loop, +;; matching each element in turn to the same pattern. The only trick +;; is that we want to keep track of the lists of each extracted id, so +;; when the loop recurses we cons the ids onto their respective list +;; variables, and on success we bind the ids (what the user input and +;; expects to see in the success body) to the reversed accumulated +;; list IDs. + +(define-syntax match-gen-ellipsis + (syntax-rules () + ((_ v p () g+s (sk ...) fk i ((id id-ls) ...)) + (match-check-identifier p + ;; simplest case equivalent to (p ...), just bind the list + (let ((p v)) + (if (list? p) + (sk ... i) + fk)) + ;; simple case, match all elements of the list + (let loop ((ls v) (id-ls '()) ...) + (cond + ((null? ls) + (let ((id (reverse id-ls)) ...) (sk ... i))) + ((pair? ls) + (let ((w (car ls))) + (match-one w p ((car ls) (set-car! ls)) + (match-drop-ids (loop (cdr ls) (cons id id-ls) ...)) + fk i))) + (else + fk))))) + ((_ v p r g+s (sk ...) fk i ((id id-ls) ...)) + ;; general case, trailing patterns to match, keep track of the + ;; remaining list length so we don't need any backtracking + (match-verify-no-ellipsis + r + (let* ((tail-len (length 'r)) + (ls v) + (len (and (list? ls) (length ls)))) + (if (or (not len) (< len tail-len)) + fk + (let loop ((ls ls) (n len) (id-ls '()) ...) + (cond + ((= n tail-len) + (let ((id (reverse id-ls)) ...) + (match-one ls r (#f #f) (sk ...) fk i))) + ((pair? ls) + (let ((w (car ls))) + (match-one w p ((car ls) (set-car! ls)) + (match-drop-ids + (loop (cdr ls) (- n 1) (cons id id-ls) ...)) + fk + i))) + (else + fk))))))))) + +;; This is just a safety check. Although unlike syntax-rules we allow +;; trailing patterns after an ellipsis, we explicitly disable multiple +;; ellipsis at the same level. This is because in the general case +;; such patterns are exponential in the number of ellipsis, and we +;; don't want to make it easy to construct very expensive operations +;; with simple looking patterns. For example, it would be O(n^2) for +;; patterns like (a ... b ...) because we must consider every trailing +;; element for every possible break for the leading "a ...". + +(define-syntax match-verify-no-ellipsis + (syntax-rules () + ((_ (x . y) sk) + (match-check-ellipsis + x + (match-syntax-error + "multiple ellipsis patterns not allowed at same level") + (match-verify-no-ellipsis y sk))) + ((_ () sk) + sk) + ((_ x sk) + (match-syntax-error "dotted tail not allowed after ellipsis" x)))) + +;; To implement the tree search, we use two recursive procedures. TRY +;; attempts to match Y once, and on success it calls the normal SK on +;; the accumulated list ids as in MATCH-GEN-ELLIPSIS. On failure, we +;; call NEXT which first checks if the current value is a list +;; beginning with X, then calls TRY on each remaining element of the +;; list. Since TRY will recursively call NEXT again on failure, this +;; effects a full depth-first search. +;; +;; The failure continuation throughout is a jump to the next step in +;; the tree search, initialized with the original failure continuation +;; FK. + +(define-syntax match-gen-search + (syntax-rules () + ((match-gen-search v p q g+s sk fk i ((id id-ls) ...)) + (letrec ((try (lambda (w fail id-ls ...) + (match-one w q g+s + (match-tuck-ids + (let ((id (reverse id-ls)) ...) + sk)) + (next w fail id-ls ...) i))) + (next (lambda (w fail id-ls ...) + (if (not (pair? w)) + (fail) + (let ((u (car w))) + (match-one + u p ((car w) (set-car! w)) + (match-drop-ids + ;; accumulate the head variables from + ;; the p pattern, and loop over the tail + (let ((id-ls (cons id id-ls)) ...) + (let lp ((ls (cdr w))) + (if (pair? ls) + (try (car ls) + (lambda () (lp (cdr ls))) + id-ls ...) + (fail))))) + (fail) i)))))) + ;; the initial id-ls binding here is a dummy to get the right + ;; number of '()s + (let ((id-ls '()) ...) + (try v (lambda () fk) id-ls ...)))))) + +;; Vector patterns are just more of the same, with the slight +;; exception that we pass around the current vector index being +;; matched. + +(define-syntax match-vector + (syntax-rules (___) + ((_ v n pats (p q) . x) + (match-check-ellipsis q + (match-gen-vector-ellipsis v n pats p . x) + (match-vector-two v n pats (p q) . x))) + ((_ v n pats (p ___) sk fk i) + (match-gen-vector-ellipsis v n pats p sk fk i)) + ((_ . x) + (match-vector-two . x)))) + +;; Check the exact vector length, then check each element in turn. + +(define-syntax match-vector-two + (syntax-rules () + ((_ v n ((pat index) ...) () sk fk i) + (if (vector? v) + (let ((len (vector-length v))) + (if (= len n) + (match-vector-step v ((pat index) ...) sk fk i) + fk)) + fk)) + ((_ v n (pats ...) (p . q) . x) + (match-vector v (+ n 1) (pats ... (p n)) q . x)))) + +(define-syntax match-vector-step + (syntax-rules () + ((_ v () (sk ...) fk i) (sk ... i)) + ((_ v ((pat index) . rest) sk fk i) + (let ((w (vector-ref v index))) + (match-one w pat ((vector-ref v index) (vector-set! v index)) + (match-vector-step v rest sk fk) + fk i))))) + +;; With a vector ellipsis pattern we first check to see if the vector +;; length is at least the required length. + +(define-syntax match-gen-vector-ellipsis + (syntax-rules () + ((_ v n ((pat index) ...) p sk fk i) + (if (vector? v) + (let ((len (vector-length v))) + (if (>= len n) + (match-vector-step v ((pat index) ...) + (match-vector-tail v p n len sk fk) + fk i) + fk)) + fk)))) + +(define-syntax match-vector-tail + (syntax-rules () + ((_ v p n len sk fk i) + (match-extract-vars p (match-vector-tail-two v p n len sk fk i) i ())))) + +(define-syntax match-vector-tail-two + (syntax-rules () + ((_ v p n len (sk ...) fk i ((id id-ls) ...)) + (let loop ((j n) (id-ls '()) ...) + (if (>= j len) + (let ((id (reverse id-ls)) ...) (sk ... i)) + (let ((w (vector-ref v j))) + (match-one w p ((vector-ref v j) (vector-set! v j)) + (match-drop-ids (loop (+ j 1) (cons id id-ls) ...)) + fk i))))))) + +(define-syntax match-record-refs + (syntax-rules () + ((_ v rec n (p . q) g+s sk fk i) + (let ((w (slot-ref rec v n))) + (match-one w p ((slot-ref rec v n) (slot-set! rec v n)) + (match-record-refs v rec (+ n 1) q g+s sk fk) fk i))) + ((_ v rec n () g+s (sk ...) fk i) + (sk ... i)))) + +(define-syntax match-record-named-refs + (syntax-rules () + ((_ v rec ((f p) . q) g+s sk fk i) + (let ((w (slot-ref rec v 'f))) + (match-one w p ((slot-ref rec v 'f) (slot-set! rec v 'f)) + (match-record-named-refs v rec q g+s sk fk) fk i))) + ((_ v rec () g+s (sk ...) fk i) + (sk ... i)))) + +;; Extract all identifiers in a pattern. A little more complicated +;; than just looking for symbols, we need to ignore special keywords +;; and non-pattern forms (such as the predicate expression in ? +;; patterns), and also ignore previously bound identifiers. +;; +;; Calls the continuation with all new vars as a list of the form +;; ((orig-var tmp-name) ...), where tmp-name can be used to uniquely +;; pair with the original variable (e.g. it's used in the ellipsis +;; generation for list variables). +;; +;; (match-extract-vars pattern continuation (ids ...) (new-vars ...)) + +(define-syntax match-extract-vars + (syntax-rules (_ ___ ..1 *** ? $ struct @ object = quote quasiquote and or not get! set!) + ((match-extract-vars (? pred . p) . x) + (match-extract-vars p . x)) + ((match-extract-vars ($ rec . p) . x) + (match-extract-vars p . x)) + ((match-extract-vars (struct rec . p) . x) + (match-extract-vars p . x)) + ((match-extract-vars (@ rec (f p) ...) . x) + (match-extract-vars (p ...) . x)) + ((match-extract-vars (object rec (f p) ...) . x) + (match-extract-vars (p ...) . x)) + ((match-extract-vars (= proc p) . x) + (match-extract-vars p . x)) + ((match-extract-vars (quote x) (k ...) i v) + (k ... v)) + ((match-extract-vars (quasiquote x) k i v) + (match-extract-quasiquote-vars x k i v (#t))) + ((match-extract-vars (and . p) . x) + (match-extract-vars p . x)) + ((match-extract-vars (or . p) . x) + (match-extract-vars p . x)) + ((match-extract-vars (not . p) . x) + (match-extract-vars p . x)) + ;; A non-keyword pair, expand the CAR with a continuation to + ;; expand the CDR. + ((match-extract-vars (p q . r) k i v) + (match-check-ellipsis + q + (match-extract-vars (p . r) k i v) + (match-extract-vars p (match-extract-vars-step (q . r) k i v) i ()))) + ((match-extract-vars (p . q) k i v) + (match-extract-vars p (match-extract-vars-step q k i v) i ())) + ((match-extract-vars #(p ...) . x) + (match-extract-vars (p ...) . x)) + ((match-extract-vars _ (k ...) i v) (k ... v)) + ((match-extract-vars ___ (k ...) i v) (k ... v)) + ((match-extract-vars *** (k ...) i v) (k ... v)) + ((match-extract-vars ..1 (k ...) i v) (k ... v)) + ;; This is the main part, the only place where we might add a new + ;; var if it's an unbound symbol. + ((match-extract-vars p (k ...) (i ...) v) + (let-syntax + ((new-sym? + (syntax-rules (i ...) + ((new-sym? p sk fk) sk) + ((new-sym? any sk fk) fk)))) + (new-sym? random-sym-to-match + (k ... ((p p-ls) . v)) + (k ... v)))) + )) + +;; Stepper used in the above so it can expand the CAR and CDR +;; separately. + +(define-syntax match-extract-vars-step + (syntax-rules () + ((_ p k i v ((v2 v2-ls) ...)) + (match-extract-vars p k (v2 ... . i) ((v2 v2-ls) ... . v))) + )) + +(define-syntax match-extract-quasiquote-vars + (syntax-rules (quasiquote unquote unquote-splicing) + ((match-extract-quasiquote-vars (quasiquote x) k i v d) + (match-extract-quasiquote-vars x k i v (#t . d))) + ((match-extract-quasiquote-vars (unquote-splicing x) k i v d) + (match-extract-quasiquote-vars (unquote x) k i v d)) + ((match-extract-quasiquote-vars (unquote x) k i v (#t)) + (match-extract-vars x k i v)) + ((match-extract-quasiquote-vars (unquote x) k i v (#t . d)) + (match-extract-quasiquote-vars x k i v d)) + ((match-extract-quasiquote-vars (x . y) k i v d) + (match-extract-quasiquote-vars + x + (match-extract-quasiquote-vars-step y k i v d) i () d)) + ((match-extract-quasiquote-vars #(x ...) k i v d) + (match-extract-quasiquote-vars (x ...) k i v d)) + ((match-extract-quasiquote-vars x (k ...) i v d) + (k ... v)) + )) + +(define-syntax match-extract-quasiquote-vars-step + (syntax-rules () + ((_ x k i v d ((v2 v2-ls) ...)) + (match-extract-quasiquote-vars x k (v2 ... . i) ((v2 v2-ls) ... . v) d)) + )) + + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Gimme some sugar baby. + +;;> Shortcut for \scheme{lambda} + \scheme{match}. Creates a +;;> procedure of one argument, and matches that argument against each +;;> clause. + +(define-syntax match-lambda + (syntax-rules () + ((_ (pattern . body) ...) (lambda (expr) (match expr (pattern . body) ...))))) + +;;> Similar to \scheme{match-lambda}. Creates a procedure of any +;;> number of arguments, and matches the argument list against each +;;> clause. + +(define-syntax match-lambda* + (syntax-rules () + ((_ (pattern . body) ...) (lambda expr (match expr (pattern . body) ...))))) + +;;> Matches each var to the corresponding expression, and evaluates +;;> the body with all match variables in scope. Raises an error if +;;> any of the expressions fail to match. Syntax analogous to named +;;> let can also be used for recursive functions which match on their +;;> arguments as in \scheme{match-lambda*}. + +(define-syntax match-let + (syntax-rules () + ((_ ((var value) ...) . body) + (match-let/helper let () () ((var value) ...) . body)) + ((_ loop ((var init) ...) . body) + (match-named-let loop ((var init) ...) . body)))) + +;;> Similar to \scheme{match-let}, but analogously to \scheme{letrec} +;;> matches and binds the variables with all match variables in scope. + +(define-syntax match-letrec + (syntax-rules () + ((_ ((var value) ...) . body) + (match-let/helper letrec () () ((var value) ...) . body)))) + +(define-syntax match-let/helper + (syntax-rules () + ((_ let ((var expr) ...) () () . body) + (let ((var expr) ...) . body)) + ((_ let ((var expr) ...) ((pat tmp) ...) () . body) + (let ((var expr) ...) + (match-let* ((pat tmp) ...) + . body))) + ((_ let (v ...) (p ...) (((a . b) expr) . rest) . body) + (match-let/helper + let (v ... (tmp expr)) (p ... ((a . b) tmp)) rest . body)) + ((_ let (v ...) (p ...) ((#(a ...) expr) . rest) . body) + (match-let/helper + let (v ... (tmp expr)) (p ... (#(a ...) tmp)) rest . body)) + ((_ let (v ...) (p ...) ((a expr) . rest) . body) + (match-let/helper let (v ... (a expr)) (p ...) rest . body)))) + +(define-syntax match-named-let + (syntax-rules () + ((_ loop ((pat expr var) ...) () . body) + (let loop ((var expr) ...) + (match-let ((pat var) ...) + . body))) + ((_ loop (v ...) ((pat expr) . rest) . body) + (match-named-let loop (v ... (pat expr tmp)) rest . body)))) + +;;> \macro{(match-let* ((var value) ...) body ...)} + +;;> Similar to \scheme{match-let}, but analogously to \scheme{let*} +;;> matches and binds the variables in sequence, with preceding match +;;> variables in scope. + +(define-syntax match-let* + (syntax-rules () + ((_ () . body) + (let () . body)) + ((_ ((pat expr) . rest) . body) + (match expr (pat (match-let* rest . body)))))) + + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Otherwise COND-EXPANDed bits. + +(cond-expand + (chibi + (define-syntax match-check-ellipsis + (er-macro-transformer + (lambda (expr rename compare) + (if (compare '... (cadr expr)) + (car (cddr expr)) + (cadr (cddr expr)))))) + (define-syntax match-check-identifier + (er-macro-transformer + (lambda (expr rename compare) + (if (identifier? (cadr expr)) + (car (cddr expr)) + (cadr (cddr expr))))))) + + (else + ;; Portable versions + ;; + ;; This *should* work, but doesn't :( + ;; (define-syntax match-check-ellipsis + ;; (syntax-rules (...) + ;; ((_ ... sk fk) sk) + ;; ((_ x sk fk) fk))) + ;; + ;; This is a little more complicated, and introduces a new let-syntax, + ;; but should work portably in any R[56]RS Scheme. Taylor Campbell + ;; originally came up with the idea. + (define-syntax match-check-ellipsis + (syntax-rules () + ;; these two aren't necessary but provide fast-case failures + ((match-check-ellipsis (a . b) success-k failure-k) failure-k) + ((match-check-ellipsis #(a ...) success-k failure-k) failure-k) + ;; matching an atom + ((match-check-ellipsis id success-k failure-k) + (let-syntax ((ellipsis? (syntax-rules () + ;; iff `id' is `...' here then this will + ;; match a list of any length + ((ellipsis? (foo id) sk fk) sk) + ((ellipsis? other sk fk) fk)))) + ;; this list of three elements will only match the (foo id) list + ;; above if `id' is `...' + (ellipsis? (a b c) success-k failure-k))))) + + ;; This is portable but can be more efficient with non-portable + ;; extensions. This trick was originally discovered by Oleg Kiselyov. + (define-syntax match-check-identifier + (syntax-rules () + ;; fast-case failures, lists and vectors are not identifiers + ((_ (x . y) success-k failure-k) failure-k) + ((_ #(x ...) success-k failure-k) failure-k) + ;; x is an atom + ((_ x success-k failure-k) + (let-syntax + ((sym? + (syntax-rules () + ;; if the symbol `abracadabra' matches x, then x is a + ;; symbol + ((sym? x sk fk) sk) + ;; otherwise x is a non-symbol datum + ((sym? y sk fk) fk)))) + (sym? abracadabra success-k failure-k)))))))