lib/match.scm: import.
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Jan Nieuwenhuizen
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911
lib/match.scm
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911
lib/match.scm
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;;;; match.scm -- portable hygienic pattern matcher -*- coding: utf-8 -*-
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;;
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;; This code is written by Alex Shinn and placed in the
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;; Public Domain. All warranties are disclaimed.
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;;> @example-import[(srfi 9)]
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;;> This is a full superset of the popular @hyperlink[
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;;> "http://www.cs.indiana.edu/scheme-repository/code.match.html"]{match}
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;;> package by Andrew Wright, written in fully portable @scheme{syntax-rules}
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;;> and thus preserving hygiene.
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;;> The most notable extensions are the ability to use @emph{non-linear}
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;;> patterns - patterns in which the same identifier occurs multiple
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;;> times, tail patterns after ellipsis, and the experimental tree patterns.
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;;> @subsubsection{Patterns}
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;;> Patterns are written to look like the printed representation of
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;;> the objects they match. The basic usage is
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;;> @scheme{(match expr (pat body ...) ...)}
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;;> where the result of @var{expr} is matched against each pattern in
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;;> turn, and the corresponding body is evaluated for the first to
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;;> succeed. Thus, a list of three elements matches a list of three
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;;> elements.
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;;> @example{(let ((ls (list 1 2 3))) (match ls ((1 2 3) #t)))}
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;;> If no patterns match an error is signalled.
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;;> Identifiers will match anything, and make the corresponding
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;;> binding available in the body.
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;;> @example{(match (list 1 2 3) ((a b c) b))}
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;;> If the same identifier occurs multiple times, the first instance
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;;> will match anything, but subsequent instances must match a value
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;;> which is @scheme{equal?} to the first.
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;;> @example{(match (list 1 2 1) ((a a b) 1) ((a b a) 2))}
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;;> The special identifier @scheme{_} matches anything, no matter how
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;;> many times it is used, and does not bind the result in the body.
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;;> @example{(match (list 1 2 1) ((_ _ b) 1) ((a b a) 2))}
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;;> To match a literal identifier (or list or any other literal), use
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;;> @scheme{quote}.
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;;> @example{(match 'a ('b 1) ('a 2))}
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;;> Analogous to its normal usage in scheme, @scheme{quasiquote} can
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;;> be used to quote a mostly literally matching object with selected
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;;> parts unquoted.
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;;> @example|{(match (list 1 2 3) (`(1 ,b ,c) (list b c)))}|
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;;> Often you want to match any number of a repeated pattern. Inside
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;;> a list pattern you can append @scheme{...} after an element to
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;;> match zero or more of that pattern (like a regexp Kleene star).
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;;> @example{(match (list 1 2) ((1 2 3 ...) #t))}
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;;> @example{(match (list 1 2 3) ((1 2 3 ...) #t))}
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;;> @example{(match (list 1 2 3 3 3) ((1 2 3 ...) #t))}
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;;> Pattern variables matched inside the repeated pattern are bound to
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;;> a list of each matching instance in the body.
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;;> @example{(match (list 1 2) ((a b c ...) c))}
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;;> @example{(match (list 1 2 3) ((a b c ...) c))}
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;;> @example{(match (list 1 2 3 4 5) ((a b c ...) c))}
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;;> More than one @scheme{...} may not be used in the same list, since
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;;> this would require exponential backtracking in the general case.
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;;> However, @scheme{...} need not be the final element in the list,
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;;> and may be succeeded by a fixed number of patterns.
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;;> @example{(match (list 1 2 3 4) ((a b c ... d e) c))}
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;;> @example{(match (list 1 2 3 4 5) ((a b c ... d e) c))}
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;;> @example{(match (list 1 2 3 4 5 6 7) ((a b c ... d e) c))}
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;;> @scheme{___} is provided as an alias for @scheme{...} when it is
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;;> inconvenient to use the ellipsis (as in a syntax-rules template).
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;;> The @scheme{..1} syntax is exactly like the @scheme{...} except
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;;> that it matches one or more repetitions (like a regexp "+").
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;;> @example{(match (list 1 2) ((a b c ..1) c))}
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;;> @example{(match (list 1 2 3) ((a b c ..1) c))}
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;;> The boolean operators @scheme{and}, @scheme{or} and @scheme{not}
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;;> can be used to group and negate patterns analogously to their
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;;> Scheme counterparts.
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;;> The @scheme{and} operator ensures that all subpatterns match.
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;;> This operator is often used with the idiom @scheme{(and x pat)} to
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;;> bind @var{x} to the entire value that matches @var{pat}
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;;> (c.f. "as-patterns" in ML or Haskell). Another common use is in
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;;> conjunction with @scheme{not} patterns to match a general case
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;;> with certain exceptions.
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;;> @example{(match 1 ((and) #t))}
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;;> @example{(match 1 ((and x) x))}
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;;> @example{(match 1 ((and x 1) x))}
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;;> The @scheme{or} operator ensures that at least one subpattern
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;;> matches. If the same identifier occurs in different subpatterns,
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;;> it is matched independently. All identifiers from all subpatterns
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;;> are bound if the @scheme{or} operator matches, but the binding is
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;;> only defined for identifiers from the subpattern which matched.
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;;> @example{(match 1 ((or) #t) (else #f))}
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;;> @example{(match 1 ((or x) x))}
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;;> @example{(match 1 ((or x 2) x))}
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;;> The @scheme{not} operator succeeds if the given pattern doesn't
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;;> match. None of the identifiers used are available in the body.
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;;> @example{(match 1 ((not 2) #t))}
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;;> The more general operator @scheme{?} can be used to provide a
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;;> predicate. The usage is @scheme{(? predicate pat ...)} where
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;;> @var{predicate} is a Scheme expression evaluating to a predicate
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;;> called on the value to match, and any optional patterns after the
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;;> predicate are then matched as in an @scheme{and} pattern.
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;;> @example{(match 1 ((? odd? x) x))}
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;;> The field operator @scheme{=} is used to extract an arbitrary
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;;> field and match against it. It is useful for more complex or
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;;> conditional destructuring that can't be more directly expressed in
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;;> the pattern syntax. The usage is @scheme{(= field pat)}, where
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;;> @var{field} can be any expression, and should result in a
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;;> procedure of one argument, which is applied to the value to match
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;;> to generate a new value to match against @var{pat}.
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;;> Thus the pattern @scheme{(and (= car x) (= cdr y))} is equivalent
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;;> to @scheme{(x . y)}, except it will result in an immediate error
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;;> if the value isn't a pair.
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;;> @example{(match '(1 . 2) ((= car x) x))}
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;;> @example{(match 4 ((= sqrt x) x))}
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;;> The record operator @scheme{$} is used as a concise way to match
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;;> records defined by SRFI-9 (or SRFI-99). The usage is
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;;> @scheme{($ rtd field ...)}, where @var{rtd} should be the record
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;;> type descriptor specified as the first argument to
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;;> @scheme{define-record-type}, and each @var{field} is a subpattern
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;;> matched against the fields of the record in order. Not all fields
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;;> must be present.
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;;> @example{
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;;> (let ()
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;;> (define-record-type employee
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;;> (make-employee name title)
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;;> employee?
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;;> (name get-name)
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;;> (title get-title))
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;;> (match (make-employee "Bob" "Doctor")
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;;> (($ employee n t) (list t n))))
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;;> }
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;;> The @scheme{set!} and @scheme{get!} operators are used to bind an
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;;> identifier to the setter and getter of a field, respectively. The
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;;> setter is a procedure of one argument, which mutates the field to
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;;> that argument. The getter is a procedure of no arguments which
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;;> returns the current value of the field.
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;;> @example{(let ((x (cons 1 2))) (match x ((1 . (set! s)) (s 3) x)))}
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;;> @example{(match '(1 . 2) ((1 . (get! g)) (g)))}
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;;> The new operator @scheme{***} can be used to search a tree for
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;;> subpatterns. A pattern of the form @scheme{(x *** y)} represents
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;;> the subpattern @var{y} located somewhere in a tree where the path
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;;> from the current object to @var{y} can be seen as a list of the
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;;> form @scheme{(x ...)}. @var{y} can immediately match the current
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;;> object in which case the path is the empty list. In a sense it's
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;;> a 2-dimensional version of the @scheme{...} pattern.
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;;> As a common case the pattern @scheme{(_ *** y)} can be used to
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;;> search for @var{y} anywhere in a tree, regardless of the path
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;;> used.
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;;> @example{(match '(a (a (a b))) ((x *** 'b) x))}
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;;> @example{(match '(a (b) (c (d e) (f g))) ((x *** 'g) x))}
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Notes
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;; The implementation is a simple generative pattern matcher - each
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;; pattern is expanded into the required tests, calling a failure
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;; continuation if the tests fail. This makes the logic easy to
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;; follow and extend, but produces sub-optimal code in cases where you
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;; have many similar clauses due to repeating the same tests.
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;; Nonetheless a smart compiler should be able to remove the redundant
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;; tests. For MATCH-LET and DESTRUCTURING-BIND type uses there is no
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;; performance hit.
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;; The original version was written on 2006/11/29 and described in the
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;; following Usenet post:
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;; http://groups.google.com/group/comp.lang.scheme/msg/0941234de7112ffd
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;; and is still available at
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;; http://synthcode.com/scheme/match-simple.scm
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;; It's just 80 lines for the core MATCH, and an extra 40 lines for
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;; MATCH-LET, MATCH-LAMBDA and other syntactic sugar.
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;;
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;; A variant of this file which uses COND-EXPAND in a few places for
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;; performance can be found at
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;; http://synthcode.com/scheme/match-cond-expand.scm
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;;
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;; 2012/05/23 - fixing combinatorial explosion of code in certain or patterns
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;; 2011/09/25 - fixing bug when directly matching an identifier repeated in
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;; the pattern (thanks to Stefan Israelsson Tampe)
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;; 2011/01/27 - fixing bug when matching tail patterns against improper lists
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;; 2010/09/26 - adding `..1' patterns (thanks to Ludovic Courtès)
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;; 2010/09/07 - fixing identifier extraction in some `...' and `***' patterns
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;; 2009/11/25 - adding `***' tree search patterns
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;; 2008/03/20 - fixing bug where (a ...) matched non-lists
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;; 2008/03/15 - removing redundant check in vector patterns
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;; 2008/03/06 - you can use `...' portably now (thanks to Taylor Campbell)
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;; 2007/09/04 - fixing quasiquote patterns
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;; 2007/07/21 - allowing ellipse patterns in non-final list positions
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;; 2007/04/10 - fixing potential hygiene issue in match-check-ellipse
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;; (thanks to Taylor Campbell)
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;; 2007/04/08 - clean up, commenting
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;; 2006/12/24 - bugfixes
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;; 2006/12/01 - non-linear patterns, shared variables in OR, get!/set!
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; force compile-time syntax errors with useful messages
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(define-syntax match-syntax-error
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(syntax-rules ()
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((_) (match-syntax-error "invalid match-syntax-error usage"))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;> @subsubsection{Syntax}
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;;> @subsubsubsection{@rawcode{(match expr (pattern . body) ...)@br{}
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;;> (match expr (pattern (=> failure) . body) ...)}}
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;;> The result of @var{expr} is matched against each @var{pattern} in
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;;> turn, according to the pattern rules described in the previous
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;;> section, until the the first @var{pattern} matches. When a match is
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;;> found, the corresponding @var{body}s are evaluated in order,
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;;> and the result of the last expression is returned as the result
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;;> of the entire @scheme{match}. If a @var{failure} is provided,
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;;> then it is bound to a procedure of no arguments which continues,
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;;> processing at the next @var{pattern}. If no @var{pattern} matches,
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;;> an error is signalled.
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;; The basic interface. MATCH just performs some basic syntax
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;; validation, binds the match expression to a temporary variable `v',
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;; and passes it on to MATCH-NEXT. It's a constant throughout the
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;; code below that the binding `v' is a direct variable reference, not
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;; an expression.
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(define-syntax match
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(syntax-rules ()
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((match)
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(match-syntax-error "missing match expression"))
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((match atom)
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(match-syntax-error "no match clauses"))
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((match (app ...) (pat . body) ...)
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(let ((v (app ...)))
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(match-next v ((app ...) (set! (app ...))) (pat . body) ...)))
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((match #(vec ...) (pat . body) ...)
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(let ((v #(vec ...)))
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(match-next v (v (set! v)) (pat . body) ...)))
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((match atom (pat . body) ...)
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(let ((v atom))
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(match-next v (atom (set! atom)) (pat . body) ...)))
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))
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;; MATCH-NEXT passes each clause to MATCH-ONE in turn with its failure
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;; thunk, which is expanded by recursing MATCH-NEXT on the remaining
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;; clauses. `g+s' is a list of two elements, the get! and set!
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;; expressions respectively.
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(define-syntax match-next
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(syntax-rules (=>)
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;; no more clauses, the match failed
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((match-next v g+s)
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;; Here we call error in non-tail context, so that the backtrace
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;; can show the source location of the failing match form.
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(begin
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(error 'match "no matching pattern" v)
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#f))
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;; named failure continuation
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((match-next v g+s (pat (=> failure) . body) . rest)
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(let ((failure (lambda () (match-next v g+s . rest))))
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;; match-one analyzes the pattern for us
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(match-one v pat g+s (match-drop-ids (begin . body)) (failure) ())))
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;; anonymous failure continuation, give it a dummy name
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((match-next v g+s (pat . body) . rest)
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(match-next v g+s (pat (=> failure) . body) . rest))))
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;; MATCH-ONE first checks for ellipse patterns, otherwise passes on to
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;; MATCH-TWO.
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(define-syntax match-one
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(syntax-rules ()
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;; If it's a list of two or more values, check to see if the
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;; second one is an ellipse and handle accordingly, otherwise go
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;; to MATCH-TWO.
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((match-one v (p q . r) g+s sk fk i)
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(match-check-ellipse
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q
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(match-extract-vars p (match-gen-ellipses v p r g+s sk fk i) i ())
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(match-two v (p q . r) g+s sk fk i)))
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;; Go directly to MATCH-TWO.
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((match-one . x)
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(match-two . x))))
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;; This is the guts of the pattern matcher. We are passed a lot of
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;; information in the form:
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;;
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;; (match-two var pattern getter setter success-k fail-k (ids ...))
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;;
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;; usually abbreviated
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;;
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;; (match-two v p g+s sk fk i)
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;;
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;; where VAR is the symbol name of the current variable we are
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;; matching, PATTERN is the current pattern, getter and setter are the
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;; corresponding accessors (e.g. CAR and SET-CAR! of the pair holding
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;; VAR), SUCCESS-K is the success continuation, FAIL-K is the failure
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;; continuation (which is just a thunk call and is thus safe to expand
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;; multiple times) and IDS are the list of identifiers bound in the
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;; pattern so far.
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(define-syntax match-two
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(syntax-rules (_ ___ ..1 *** quote quasiquote ? $ = and or not set! get!)
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((match-two v () g+s (sk ...) fk i)
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(if (null? v) (sk ... i) fk))
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((match-two v (quote p) g+s (sk ...) fk i)
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(if (equal? v 'p) (sk ... i) fk))
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((match-two v (quasiquote p) . x)
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(match-quasiquote v p . x))
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((match-two v (and) g+s (sk ...) fk i) (sk ... i))
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((match-two v (and p q ...) g+s sk fk i)
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(match-one v p g+s (match-one v (and q ...) g+s sk fk) fk i))
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((match-two v (or) g+s sk fk i) fk)
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((match-two v (or p) . x)
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(match-one v p . x))
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((match-two v (or p ...) g+s sk fk i)
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(match-extract-vars (or p ...) (match-gen-or v (p ...) g+s sk fk i) i ()))
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((match-two v (not p) g+s (sk ...) fk i)
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(match-one v p g+s (match-drop-ids fk) (sk ... i) i))
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((match-two v (get! getter) (g s) (sk ...) fk i)
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(let ((getter (lambda () g))) (sk ... i)))
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((match-two v (set! setter) (g (s ...)) (sk ...) fk i)
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(let ((setter (lambda (x) (s ... x)))) (sk ... i)))
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((match-two v (? pred . p) g+s sk fk i)
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(if (pred v) (match-one v (and . p) g+s sk fk i) fk))
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((match-two v (= proc p) . x)
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(let ((w (proc v))) (match-one w p . x)))
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((match-two v (p ___ . r) g+s sk fk i)
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(match-extract-vars p (match-gen-ellipses v p r g+s sk fk i) i ()))
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((match-two v (p) g+s sk fk i)
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(if (and (pair? v) (null? (cdr v)))
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(let ((w (car v)))
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(match-one w p ((car v) (set-car! v)) sk fk i))
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fk))
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((match-two v (p *** q) g+s sk fk i)
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(match-extract-vars p (match-gen-search v p q g+s sk fk i) i ()))
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((match-two v (p *** . q) g+s sk fk i)
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(match-syntax-error "invalid use of ***" (p *** . q)))
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((match-two v (p ..1) g+s sk fk i)
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(if (pair? v)
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(match-one v (p ___) g+s sk fk i)
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fk))
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((match-two v ($ rec p ...) g+s sk fk i)
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(if (is-a? v rec)
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(match-record-refs v rec 0 (p ...) g+s sk fk i)
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fk))
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((match-two v (p . q) g+s sk fk i)
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(if (pair? v)
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(let ((w (car v)) (x (cdr v)))
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(match-one w p ((car v) (set-car! v))
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(match-one x q ((cdr v) (set-cdr! v)) sk fk)
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fk
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i))
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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-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, keep track of the
|
||||
;; remaining list length so we don't need any backtracking
|
||||
(match-verify-no-ellipses
|
||||
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 ellipses, 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-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)))
|
||||
((_ () sk)
|
||||
sk)
|
||||
((_ x sk)
|
||||
(match-syntax-error "dotted tail not allowed after ellipse" 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-ELLIPSES. 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-ellipse q
|
||||
(match-gen-vector-ellipses v n pats p . x)
|
||||
(match-vector-two v n pats (p q) . x)))
|
||||
((_ v n pats (p ___) sk fk i)
|
||||
(match-gen-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) . 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 ellipse pattern we first check to see if the vector
|
||||
;; length is at least the required length.
|
||||
|
||||
(define-syntax match-gen-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)))))))
|
||||
|
||||
(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 ellipse
|
||||
;; 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-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 ...) . 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 (#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.
|
||||
|
||||
;;> 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)
|
||||
(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)))))
|
||||
Loading…
Reference in a new issue