;;;; 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)] | |
;;> 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. | |
;;> @subsubsection{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 signaled. | |
;;> 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 ((= sqrt 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)))) | |
;;> } | |
;;> 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 | |
;; | |
;; 2021/06/21 - fix for `(a ...)' patterns where `a' is already bound | |
;; (thanks to Andy Wingo) | |
;; 2020/09/04 - [OMITTED IN GUILE] perf fix for `not`; rename `..=', `..=', `..1' per SRFI 204 | |
;; 2020/08/21 - [OMITTED IN GUILE] fixing match-letrec with unhygienic insertion | |
;; 2020/07/06 - [OMITTED IN GUILE] adding `..=' and `..=' patterns; fixing ,@ patterns | |
;; 2016/10/05 - [OMITTED IN GUILE] treat keywords as literals, not identifiers, in Chicken | |
;; 2016/03/06 - fixing named match-let (thanks to Stefan Israelsson Tampe) | |
;; 2015/05/09 - fixing bug in var extraction of quasiquote patterns | |
;; 2014/11/24 - [OMITTED IN GUILE] 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")))) | |
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; | |
;;> @subsubsection{Syntax} | |
;;> @subsubsubsection{@rawcode{(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 signaled. | |
;; 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) | |
;; Here we call error in non-tail context, so that the backtrace | |
;; can show the source location of the failing match form. | |
(begin | |
(throw 'match-error "match" "no matching pattern" v) | |
#f)) | |
;; 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 ? $ = 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 (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 ((w v)) | |
(if (list? w) | |
(match-one w p g+s (sk ...) fk 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) ...)) | |
(match-verify-no-ellipsis | |
r | |
(match-bound-identifier-memv | |
p | |
(i ...) | |
;; p is bound, match the list up to the known length, then | |
;; match the trailing patterns | |
(let loop ((ls v) (expect p)) | |
(cond | |
((null? expect) | |
(match-one ls r (#f #f) sk fk (i ...))) | |
((pair? ls) | |
(let ((w (car ls)) | |
(e (car expect))) | |
(if (equal? (car ls) (car expect)) | |
(match-drop-ids (loop (cdr ls) (cdr expect))) | |
fk))) | |
(else | |
fk))) | |
;; general case, trailing patterns to match, keep track of the | |
;; remaining list length so we don't need any backtracking | |
(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 ... id ...)))) | |
((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 | |
;; ellipses at the same level. This is because in the general case | |
;; such patterns are exponential in the number of ellipses, 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)))) | |
;; 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 *** ? $ = 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 (= 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)))) | |
;;> @subsubsubsection{@rawcode{(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. | |
;; 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))))) | |
(define-syntax match-bound-identifier-memv | |
(syntax-rules () | |
((match-bound-identifier-memv a (id ...) sk fk) | |
(match-check-identifier | |
a | |
(let-syntax | |
((memv? | |
(syntax-rules (id ...) | |
((memv? a sk2 fk2) fk2) | |
((memv? anything-else sk2 fk2) sk2)))) | |
(memv? random-sym-to-match sk fk)) | |
fk)))) | |