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foof/match.scm
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[112a40d018]
at
2016-09-01 08:27:10
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— various improvements, added lmdb , added license notices
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;;;; match.scm -- portable hygienic pattern matcher
;;
;; This code is written by Alex Shinn and placed in the
;; Public Domain. All warranties are disclaimed.
;; This is a full superset of the popular MATCH package by Andrew
;; Wright, written in fully portable SYNTAX-RULES (R5RS only, breaks
;; in R6RS SYNTAX-RULES), and thus preserving hygiene.
;; This 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
;; A variant of this file which uses COND-EXPAND in a few places can
;; be found at
;; http://synthcode.com/scheme/match-cond-expand.scm
;;
;; 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 ellipse patterns in non-final list positions
;; 2007/04/10 - fixing potential hygiene issue in match-check-ellipse
;; (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"))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 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 "missing match clause"))
((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) ...)
(match-next atom 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' and `s' are 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 ellipse patterns, otherwise passes on to
;; MATCH-TWO.
(define-syntax match-one
(syntax-rules ()
;; If it's a list of two values, check to see if the second one is
;; an ellipse and handle accordingly, otherwise go to MATCH-TWO.
((match-one v (p q . r) g s sk fk i)
(match-check-ellipse
q
(match-extract-vars p (match-gen-ellipses v p r g s sk fk i) i ())
(match-two v (p q . r) g s sk fk i)))
;; Otherwise, 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 (_ ___ 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) g s sk fk i)
(match-quasiquote v p g s sk fk i))
((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) g s sk fk i)
(match-one v p g s sk fk i))
((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) g s sk fk i)
(let ((w (proc v)))
(match-one w p g s sk fk i)))
((match-two v (p ___ . r) g s sk fk i)
(match-extract-vars p (match-gen-ellipses 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)
(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 sk fk i)
(match-vector v 0 () (p ...) sk fk i))
((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
;; A CPS utility that takes two values and just expands into the
;; first.
(define-syntax match-drop-ids
(syntax-rules ()
((_ expr ids ...) expr)))
;; Generating OR clauses just involves binding the success
;; continuation into a thunk which takes the identifiers common to
;; each OR clause, and trying each clause, calling the thunk as soon
;; as we succeed.
(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 i)
;; no OR clauses, call the failure continuation
fk)
((_ v (p) g s sk fk i)
;; last (or only) OR clause, just expand normally
(match-one v p g s sk fk i))
((_ v (p . q) g s sk fk i)
;; match one and try the remaining on failure
(match-one v p g s sk (match-gen-or-step v q g s sk fk i) 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 - it's just a named let loop, matching each
;; element in turn to the same pattern. This illustrates the
;; simplicity of this generative-style pattern matching. It would be
;; just as easy to implement a tree searching pattern.
(define-syntax match-gen-ellipses
(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
(match-verify-no-ellipses
(r ...)
(let* ((tail-len (length '(r ...)))
(ls v)
(len (length ls)))
(if (< 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 ... i) 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)))))))
))
(define-syntax match-verify-no-ellipses
(syntax-rules ()
((_ (x . y) sk)
(match-check-ellipse
x
(match-syntax-error
"multiple ellipse patterns not allowed at same level")
(match-verify-no-ellipses y sk)))
((_ x sk) sk)
))
;; 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) sk fk i)
(match-check-ellipse q
(match-vector-ellipses v n pats p sk fk i)
(match-vector-two v n pats (p q) sk fk i)))
((_ v n pats (p ___) sk fk i)
(match-vector-ellipses 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) sk fk i)
(match-vector v (+ n 1) (pats ... (p n)) q sk fk i))
))
(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 ellipse pattern we first check to see if the vector
;; length is at least the required length.
(define-syntax match-vector-ellipses
(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) (vetor-set! v j)
(match-drop-ids (loop (+ j 1) (cons id id-ls) ...))
fk i)))))))
;; Extract all identifiers in a pattern. A little more complicated
;; than just looking for symbols, we need to ignore special keywords
;; and not pattern forms (such as the predicate expression in ?
;; patterns).
;;
;; (match-extract-vars pattern continuation (ids ...) (new-vars ...))
(define-syntax match-extract-vars
(syntax-rules (_ ___ ? $ = quote quasiquote and or not get! set!)
((match-extract-vars (? pred . p) k i v)
(match-extract-vars p k i v))
((match-extract-vars ($ rec . p) k i v)
(match-extract-vars p k i v))
((match-extract-vars (= proc p) k i v)
(match-extract-vars p k i v))
((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) k i v)
(match-extract-vars p k i v))
((match-extract-vars (or . p) k i v)
(match-extract-vars p k i v))
((match-extract-vars (not . p) k i v)
(match-extract-vars p k i v))
;; 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-ellipse
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 ...) k i v)
(match-extract-vars (p ...) k i v))
((match-extract-vars _ (k ...) i v) (k ... v))
((match-extract-vars ___ (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? x 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 (#t . d))
(match-extract-quasiquote-vars
x
(match-extract-quasiquote-vars-step y k i v d) i ()))
((match-extract-quasiquote-vars #(x ...) k i v (#t . d))
(match-extract-quasiquote-vars (x ...) k i v d))
((match-extract-quasiquote-vars x (k ...) i v (#t . 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.
(define-syntax match-lambda
(syntax-rules ()
((_ clause ...) (lambda (expr) (match expr clause ...)))))
(define-syntax match-lambda*
(syntax-rules ()
((_ clause ...) (lambda expr (match expr clause ...)))))
(define-syntax match-let
(syntax-rules ()
((_ (vars ...) . body)
(match-let/helper let () () (vars ...) . body))
((_ loop . rest)
(match-named-let loop () . rest))))
(define-syntax match-letrec
(syntax-rules ()
((_ vars . body) (match-let/helper letrec () () vars . 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))))
(define-syntax match-let*
(syntax-rules ()
((_ () . body)
(begin . 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-ellipse
;; (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-ellipse
(syntax-rules ()
;; these two aren't necessary but provide fast-case failures
((match-check-ellipse (a . b) success-k failure-k) failure-k)
((match-check-ellipse #(a ...) success-k failure-k) failure-k)
;; matching an atom
((match-check-ellipse id success-k failure-k)
(let-syntax ((ellipse? (syntax-rules ()
;; iff `id' is `...' here then this will
;; match a list of any length
((ellipse? (foo id) sk fk) sk)
((ellipse? other sk fk) fk))))
;; this list of three elements will only many the (foo id) list
;; above if `id' is `...'
(ellipse? (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)))
))