-;;; -*- lexical-binding: t -*-
-;;; pcase.el --- ML-style pattern-matching macro for Elisp
+;;; pcase.el --- ML-style pattern-matching macro for Elisp -*- lexical-binding: t -*-
-;; Copyright (C) 2010-2011 Free Software Foundation, Inc.
+;; Copyright (C) 2010-2012 Free Software Foundation, Inc.
;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
-;; Keywords:
+;; Keywords:
;; This file is part of GNU Emacs.
;; Todo:
+;; - (pcase e (`(,x . ,x) foo)) signals an "x unused" warning if `foo' doesn't
+;; use x, because x is bound separately for the equality constraint
+;; (as well as any pred/guard) and for the body, so uses at one place don't
+;; count for the other.
;; - provide ways to extend the set of primitives, with some kind of
;; define-pcase-matcher. We could easily make it so that (guard BOOLEXP)
;; could be defined this way, as a shorthand for (pred (lambda (_) BOOLEXP)).
;; But better would be if we could define new ways to match by having the
;; extension provide its own `pcase--split-<foo>' thingy.
+;; - along these lines, provide patterns to match CL structs.
+;; - provide something like (setq VAR) so a var can be set rather than
+;; let-bound.
+;; - provide a way to fallthrough to subsequent cases.
+;; - try and be more clever to reduce the size of the decision tree, and
+;; to reduce the number of leaves that need to be turned into function:
+;; - first, do the tests shared by all remaining branches (it will have
+;; to be performed anyway, so better so it first so it's shared).
+;; - then choose the test that discriminates more (?).
;; - ideally we'd want (pcase s ((re RE1) E1) ((re RE2) E2)) to be able to
;; generate a lex-style DFA to decide whether to run E1 or E2.
;;; Code:
-(eval-when-compile (require 'cl))
-
;; Macro-expansion of pcase is reasonably fast, so it's not a problem
;; when byte-compiling a file, but when interpreting the code, if the pcase
;; is in a loop, the repeated macro-expansion becomes terribly costly, so we
;; memoize previous macro expansions to try and avoid recomputing them
;; over and over again.
-(defconst pcase-memoize (make-hash-table :weakness t :test 'equal))
+(defconst pcase--memoize (make-hash-table :weakness 'key :test 'eq))
(defconst pcase--dontcare-upats '(t _ dontcare))
`QPAT matches if the QPattern QPAT matches.
(pred PRED) matches if PRED applied to the object returns non-nil.
(guard BOOLEXP) matches if BOOLEXP evaluates to non-nil.
+ (let UPAT EXP) matches if EXP matches UPAT.
+If a SYMBOL is used twice in the same pattern (i.e. the pattern is
+\"non-linear\"), then the second occurrence is turned into an `eq'uality test.
QPatterns can take the following forms:
(QPAT1 . QPAT2) matches if QPAT1 matches the car and QPAT2 the cdr.
,UPAT matches if the UPattern UPAT matches.
- STRING matches if the object is `equal' to STRING.
+ STRING matches if the object is `equal' to STRING.
ATOM matches if the object is `eq' to ATOM.
QPatterns for vectors are not implemented yet.
PRED can take the form
- FUNCTION in which case it gets called with one argument.
+ FUNCTION in which case it gets called with one argument.
(FUN ARG1 .. ARGN) in which case it gets called with N+1 arguments.
A PRED of the form FUNCTION is equivalent to one of the form (FUNCTION).
PRED patterns can refer to variables bound earlier in the pattern.
like `(,a . ,(pred (< a))) or, with more checks:
`(,(and a (pred numberp)) . ,(and (pred numberp) (pred (< a))))"
(declare (indent 1) (debug case)) ;FIXME: edebug `guard' and vars.
- (or (gethash (cons exp cases) pcase-memoize)
- (puthash (cons exp cases)
- (pcase--expand exp cases)
- pcase-memoize)))
+ ;; We want to use a weak hash table as a cache, but the key will unavoidably
+ ;; be based on `exp' and `cases', yet `cases' is a fresh new list each time
+ ;; we're called so it'll be immediately GC'd. So we use (car cases) as key
+ ;; which does come straight from the source code and should hence not be GC'd
+ ;; so easily.
+ (let ((data (gethash (car cases) pcase--memoize)))
+ ;; data = (EXP CASES . EXPANSION)
+ (if (and (equal exp (car data)) (equal cases (cadr data)))
+ ;; We have the right expansion.
+ (cddr data)
+ (when data
+ (message "pcase-memoize: equal first branch, yet different"))
+ (let ((expansion (pcase--expand exp cases)))
+ (puthash (car cases) (cons exp (cons cases expansion)) pcase--memoize)
+ expansion))))
;;;###autoload
(defmacro pcase-let* (bindings &rest body)
"Like `let*' but where you can use `pcase' patterns for bindings.
BODY should be an expression, and BINDINGS should be a list of bindings
of the form (UPAT EXP)."
- (declare (indent 1) (debug let))
+ (declare (indent 1)
+ (debug ((&rest &or (sexp &optional form) symbolp) body)))
(cond
((null bindings) (if (> (length body) 1) `(progn ,@body) (car body)))
((pcase--trivial-upat-p (caar bindings))
"Like `let' but where you can use `pcase' patterns for bindings.
BODY should be a list of expressions, and BINDINGS should be a list of bindings
of the form (UPAT EXP)."
- (declare (indent 1) (debug let))
+ (declare (indent 1) (debug pcase-let*))
(if (null (cdr bindings))
`(pcase-let* ,bindings ,@body)
(let ((matches '()))
`(let ,(nreverse bindings) (pcase-let* ,matches ,@body)))))
(defmacro pcase-dolist (spec &rest body)
+ (declare (indent 1))
(if (pcase--trivial-upat-p (car spec))
`(dolist ,spec ,@body)
(let ((tmpvar (make-symbol "x")))
(and (symbolp upat) (not (memq upat pcase--dontcare-upats))))
(defun pcase--expand (exp cases)
+ ;; (message "pid=%S (pcase--expand %S ...hash=%S)"
+ ;; (emacs-pid) exp (sxhash cases))
(let* ((defs (if (symbolp exp) '()
(let ((sym (make-symbol "x")))
(prog1 `((,sym ,exp)) (setq exp sym)))))
;; to a separate function if that number is too high.
;;
;; We've already used this branch. So it is shared.
- (destructuring-bind (code prevvars res) prev
+ (let* ((code (car prev)) (cdrprev (cdr prev))
+ (prevvars (car cdrprev)) (cddrprev (cdr cdrprev))
+ (res (car cddrprev)))
(unless (symbolp res)
;; This is the first repeat, so we have to move
;; the branch to a separate function.
(cdr case))))
cases))))
(if (null defs) main
- `(let ,defs ,main))))
+ (pcase--let* defs main))))
(defun pcase-codegen (code vars)
- `(let ,(mapcar (lambda (b) (list (car b) (cdr b))) vars)
+ `(let* ,(mapcar (lambda (b) (list (car b) (cdr b))) vars)
,@code))
(defun pcase--small-branch-p (code)
(defun pcase--if (test then else)
(cond
((eq else :pcase--dontcare) then)
+ ((eq then :pcase--dontcare) (debug) else) ;Can/should this ever happen?
((eq (car-safe else) 'if)
(if (equal test (nth 1 else))
;; Doing a test a second time: get rid of the redundancy.
`(cond (,test ,then)
;; Doing a test a second time: get rid of the redundancy, as above.
,@(remove (assoc test else) (cdr else))))
+ ;; Invert the test if that lets us reduce the depth of the tree.
+ ((memq (car-safe then) '(if cond)) (pcase--if `(not ,test) else then))
(t `(if ,test ,then ,else))))
+;; Again, try and reduce nesting.
+(defun pcase--let* (binders body)
+ (if (eq (car-safe body) 'let*)
+ `(let* ,(append binders (nth 1 body))
+ ,@(nthcdr 2 body))
+ `(let* ,binders ,body)))
+
(defun pcase--upat (qpattern)
(cond
((eq (car-safe qpattern) '\,) (cadr qpattern))
(and MATCH ...)
(or MATCH ...)"
(when (setq branches (delq nil branches))
- (destructuring-bind (match code &rest vars) (car branches)
+ (let* ((carbranch (car branches))
+ (match (car carbranch)) (cdarbranch (cdr carbranch))
+ (code (car cdarbranch))
+ (vars (cdr cdarbranch)))
(pcase--u1 (list match) code vars (cdr branches)))))
(defun pcase--and (match matches)
(if matches `(and ,match ,@matches) match))
+(defconst pcase-mutually-exclusive-predicates
+ '((symbolp . integerp)
+ (symbolp . numberp)
+ (symbolp . consp)
+ (symbolp . arrayp)
+ (symbolp . stringp)
+ (symbolp . byte-code-function-p)
+ (integerp . consp)
+ (integerp . arrayp)
+ (integerp . stringp)
+ (integerp . byte-code-function-p)
+ (numberp . consp)
+ (numberp . arrayp)
+ (numberp . stringp)
+ (numberp . byte-code-function-p)
+ (consp . arrayp)
+ (consp . stringp)
+ (consp . byte-code-function-p)
+ (arrayp . stringp)
+ (arrayp . byte-code-function-p)
+ (stringp . byte-code-function-p)))
+
(defun pcase--split-match (sym splitter match)
- (case (car match)
- ((match)
+ (cond
+ ((eq (car match) 'match)
(if (not (eq sym (cadr match)))
(cons match match)
(let ((pat (cddr match)))
(cdr pat)))))
(t (let ((res (funcall splitter (cddr match))))
(cons (or (car res) match) (or (cdr res) match))))))))
- ((or and)
+ ((memq (car match) '(or and))
(let ((then-alts '())
(else-alts '())
(neutral-elem (if (eq 'or (car match))
(dolist (branch rest)
(let* ((match (car branch))
(code&vars (cdr branch))
- (splitted
+ (split
(pcase--split-match sym splitter match)))
- (unless (eq (car splitted) :pcase--fail)
- (push (cons (car splitted) code&vars) then-rest))
- (unless (eq (cdr splitted) :pcase--fail)
- (push (cons (cdr splitted) code&vars) else-rest))))
+ (unless (eq (car split) :pcase--fail)
+ (push (cons (car split) code&vars) then-rest))
+ (unless (eq (cdr split) :pcase--fail)
+ (push (cons (cdr split) code&vars) else-rest))))
(cons (nreverse then-rest) (nreverse else-rest))))
(defun pcase--split-consp (syma symd pat)
(cons `(and (match ,syma . ,(pcase--upat (car qpat)))
(match ,symd . ,(pcase--upat (cdr qpat))))
:pcase--fail)))
- ;; A QPattern but not for a cons, can only go the `else' side.
- ((eq (car-safe pat) '\`) (cons :pcase--fail nil))))
+ ;; A QPattern but not for a cons, can only go to the `else' side.
+ ((eq (car-safe pat) '\`) (cons :pcase--fail nil))
+ ((and (eq (car-safe pat) 'pred)
+ (or (member (cons 'consp (cadr pat))
+ pcase-mutually-exclusive-predicates)
+ (member (cons (cadr pat) 'consp)
+ pcase-mutually-exclusive-predicates)))
+ (cons :pcase--fail nil))))
(defun pcase--split-equal (elem pat)
(cond
;; (or (integerp (cadr pat)) (symbolp (cadr pat))
;; (consp (cadr pat)))
)
- (cons :pcase--fail nil))))
+ (cons :pcase--fail nil))
+ ((and (eq (car-safe pat) 'pred)
+ (symbolp (cadr pat))
+ (get (cadr pat) 'side-effect-free)
+ (funcall (cadr pat) elem))
+ (cons :pcase--succeed nil))))
(defun pcase--split-member (elems pat)
;; Based on pcase--split-equal.
;; (or (integerp (cadr pat)) (symbolp (cadr pat))
;; (consp (cadr pat)))
)
- (cons :pcase--fail nil))))
+ (cons :pcase--fail nil))
+ ((and (eq (car-safe pat) 'pred)
+ (symbolp (cadr pat))
+ (get (cadr pat) 'side-effect-free)
+ (let ((p (cadr pat)) (all t))
+ (dolist (elem elems)
+ (unless (funcall p elem) (setq all nil)))
+ all))
+ (cons :pcase--succeed nil))))
(defun pcase--split-pred (upat pat)
;; FIXME: For predicates like (pred (> a)), two such predicates may
;; actually refer to different variables `a'.
- (if (equal upat pat)
- (cons :pcase--succeed :pcase--fail)))
+ (let (test)
+ (cond
+ ((equal upat pat) (cons :pcase--succeed :pcase--fail))
+ ((and (eq 'pred (car upat))
+ (eq 'pred (car-safe pat))
+ (or (member (cons (cadr upat) (cadr pat))
+ pcase-mutually-exclusive-predicates)
+ (member (cons (cadr pat) (cadr upat))
+ pcase-mutually-exclusive-predicates)))
+ (cons :pcase--fail nil))
+ ((and (eq 'pred (car upat))
+ (eq '\` (car-safe pat))
+ (symbolp (cadr upat))
+ (or (symbolp (cadr pat)) (stringp (cadr pat)) (numberp (cadr pat)))
+ (get (cadr upat) 'side-effect-free)
+ (ignore-errors
+ (setq test (list (funcall (cadr upat) (cadr pat))))))
+ (if (car test)
+ (cons nil :pcase--fail)
+ (cons :pcase--fail nil))))))
(defun pcase--fgrep (vars sexp)
"Check which of the symbols VARS appear in SEXP."
;; bootstrapping problems.
(defun pcase--u1 (matches code vars rest)
"Return code that runs CODE (with VARS) if MATCHES match.
-and otherwise defers to REST which is a list of branches of the form
+Otherwise, it defers to REST which is a list of branches of the form
\(ELSE-MATCH ELSE-CODE . ELSE-VARS)."
;; Depending on the order in which we choose to check each of the MATCHES,
;; the resulting tree may be smaller or bigger. So in general, we'd want
(pcase--u1 (cons `(match ,var or . ,(nreverse simples)) (cdr matches))
code vars
(if (null others) rest
- (cons (list*
+ (cons (cons
(pcase--and (if (cdr others)
(cons 'or (nreverse others))
(car others))
(cdr matches))
- code vars)
+ (cons code vars))
rest))))
(t
(pcase--u1 (cons (pop alts) (cdr matches)) code vars
(if (null alts) (progn (error "Please avoid it") rest)
- (cons (list*
+ (cons (cons
(pcase--and (if (cdr alts)
(cons 'or alts) (car alts))
(cdr matches))
- code vars)
+ (cons code vars))
rest)))))))
((eq 'match (caar matches))
- (destructuring-bind (op sym &rest upat) (pop matches)
+ (let* ((popmatches (pop matches))
+ (_op (car popmatches)) (cdrpopmatches (cdr popmatches))
+ (sym (car cdrpopmatches))
+ (upat (cdr cdrpopmatches)))
(cond
((memq upat '(t _)) (pcase--u1 matches code vars rest))
((eq upat 'dontcare) :pcase--dontcare)
- ((functionp upat) (error "Feature removed, use (pred %s)" upat))
((memq (car-safe upat) '(guard pred))
- (destructuring-bind (then-rest &rest else-rest)
- (pcase--split-rest
- sym (apply-partially #'pcase--split-pred upat) rest)
+ (if (eq (car upat) 'pred) (put sym 'pcase-used t))
+ (let* ((splitrest
+ (pcase--split-rest
+ sym (apply-partially #'pcase--split-pred upat) rest))
+ (then-rest (car splitrest))
+ (else-rest (cdr splitrest)))
(pcase--if (if (and (eq (car upat) 'pred) (symbolp (cadr upat)))
`(,(cadr upat) ,sym)
(let* ((exp (cadr upat))
;; `vs' is an upper bound on the vars we need.
(vs (pcase--fgrep (mapcar #'car vars) exp))
- (call (cond
- ((eq 'guard (car upat)) exp)
- ((functionp exp) `(,exp ,sym))
- (t `(,@exp ,sym)))))
+ (env (mapcar (lambda (var)
+ (list var (cdr (assq var vars))))
+ vs))
+ (call (if (eq 'guard (car upat))
+ exp
+ (when (memq sym vs)
+ ;; `sym' is shadowed by `env'.
+ (let ((newsym (make-symbol "x")))
+ (push (list newsym sym) env)
+ (setq sym newsym)))
+ (if (functionp exp) `(,exp ,sym)
+ `(,@exp ,sym)))))
(if (null vs)
call
;; Let's not replace `vars' in `exp' since it's
;; too difficult to do it right, instead just
;; let-bind `vars' around `exp'.
- `(let ,(mapcar (lambda (var)
- (list var (cdr (assq var vars))))
- vs)
- ;; FIXME: `vars' can capture `sym'. E.g.
- ;; (pcase x ((and `(,x . ,y) (pred (fun x)))))
- ,call))))
+ `(let* ,env ,call))))
(pcase--u1 matches code vars then-rest)
(pcase--u else-rest))))
((symbolp upat)
- (pcase--u1 matches code (cons (cons upat sym) vars) rest))
+ (put sym 'pcase-used t)
+ (if (not (assq upat vars))
+ (pcase--u1 matches code (cons (cons upat sym) vars) rest)
+ ;; Non-linear pattern. Turn it into an `eq' test.
+ (pcase--u1 (cons `(match ,sym . (pred (eq ,(cdr (assq upat vars)))))
+ matches)
+ code vars rest)))
+ ((eq (car-safe upat) 'let)
+ ;; A upat of the form (let VAR EXP).
+ ;; (pcase--u1 matches code
+ ;; (cons (cons (nth 1 upat) (nth 2 upat)) vars) rest)
+ (let* ((exp
+ (let* ((exp (nth 2 upat))
+ (found (assq exp vars)))
+ (if found (cdr found)
+ (let* ((vs (pcase--fgrep (mapcar #'car vars) exp))
+ (env (mapcar (lambda (v) (list v (cdr (assq v vars))))
+ vs)))
+ (if env `(let* ,env ,exp) exp)))))
+ (sym (if (symbolp exp) exp (make-symbol "x")))
+ (body
+ (pcase--u1 (cons `(match ,sym . ,(nth 1 upat)) matches)
+ code vars rest)))
+ (if (eq sym exp)
+ body
+ `(let* ((,sym ,exp)) ,body))))
((eq (car-safe upat) '\`)
+ (put sym 'pcase-used t)
(pcase--q1 sym (cadr upat) matches code vars rest))
((eq (car-safe upat) 'or)
(let ((all (> (length (cdr upat)) 1))
(setq all nil))))
(if all
;; Use memq for (or `a `b `c `d) rather than a big tree.
- (let ((elems (mapcar 'cadr (cdr upat))))
- (destructuring-bind (then-rest &rest else-rest)
- (pcase--split-rest
- sym (apply-partially #'pcase--split-member elems) rest)
- (pcase--if `(,(if memq-fine #'memq #'member) ,sym ',elems)
- (pcase--u1 matches code vars then-rest)
- (pcase--u else-rest))))
+ (let* ((elems (mapcar 'cadr (cdr upat)))
+ (splitrest
+ (pcase--split-rest
+ sym (apply-partially #'pcase--split-member elems) rest))
+ (then-rest (car splitrest))
+ (else-rest (cdr splitrest)))
+ (pcase--if `(,(if memq-fine #'memq #'member) ,sym ',elems)
+ (pcase--u1 matches code vars then-rest)
+ (pcase--u else-rest)))
(pcase--u1 (cons `(match ,sym ,@(cadr upat)) matches) code vars
(append (mapcar (lambda (upat)
`((and (match ,sym . ,upat) ,@matches)
(pcase--u1 `((match ,sym . ,(cadr upat)))
;; FIXME: This codegen is not careful to share its
;; code if used several times: code blow up is likely.
- (lambda (vars)
+ (lambda (_vars)
;; `vars' will likely contain bindings which are
;; not always available in other paths to
;; `rest', so there' no point trying to pass
(defun pcase--q1 (sym qpat matches code vars rest)
"Return code that runs CODE if SYM matches QPAT and if MATCHES match.
-and if not, defers to REST which is a list of branches of the form
+Otherwise, it defers to REST which is a list of branches of the form
\(OTHER_MATCH OTHER-CODE . OTHER-VARS)."
(cond
((eq (car-safe qpat) '\,) (error "Can't use `,UPATTERN"))
;; FIXME.
(error "Vector QPatterns not implemented yet"))
((consp qpat)
- (let ((syma (make-symbol "xcar"))
- (symd (make-symbol "xcdr")))
- (destructuring-bind (then-rest &rest else-rest)
- (pcase--split-rest sym
- (apply-partially #'pcase--split-consp syma symd)
- rest)
- (pcase--if `(consp ,sym)
- `(let ((,syma (car ,sym))
- (,symd (cdr ,sym)))
- ,(pcase--u1 `((match ,syma . ,(pcase--upat (car qpat)))
- (match ,symd . ,(pcase--upat (cdr qpat)))
- ,@matches)
- code vars then-rest))
- (pcase--u else-rest)))))
+ (let* ((syma (make-symbol "xcar"))
+ (symd (make-symbol "xcdr"))
+ (splitrest (pcase--split-rest
+ sym
+ (apply-partially #'pcase--split-consp syma symd)
+ rest))
+ (then-rest (car splitrest))
+ (else-rest (cdr splitrest))
+ (then-body (pcase--u1 `((match ,syma . ,(pcase--upat (car qpat)))
+ (match ,symd . ,(pcase--upat (cdr qpat)))
+ ,@matches)
+ code vars then-rest)))
+ (pcase--if
+ `(consp ,sym)
+ ;; We want to be careful to only add bindings that are used.
+ ;; The byte-compiler could do that for us, but it would have to pay
+ ;; attention to the `consp' test in order to figure out that car/cdr
+ ;; can't signal errors and our byte-compiler is not that clever.
+ ;; FIXME: Some of those let bindings occur too early (they are used in
+ ;; `then-body', but only within some sub-branch).
+ (pcase--let*
+ `(,@(if (get syma 'pcase-used) `((,syma (car ,sym))))
+ ,@(if (get symd 'pcase-used) `((,symd (cdr ,sym)))))
+ then-body)
+ (pcase--u else-rest))))
((or (integerp qpat) (symbolp qpat) (stringp qpat))
- (destructuring-bind (then-rest &rest else-rest)
- (pcase--split-rest sym (apply-partially 'pcase--split-equal qpat) rest)
- (pcase--if `(,(if (stringp qpat) #'equal #'eq) ,sym ',qpat)
+ (let* ((splitrest (pcase--split-rest
+ sym (apply-partially 'pcase--split-equal qpat) rest))
+ (then-rest (car splitrest))
+ (else-rest (cdr splitrest)))
+ (pcase--if (cond
+ ((stringp qpat) `(equal ,sym ,qpat))
+ ((null qpat) `(null ,sym))
+ (t `(eq ,sym ',qpat)))
(pcase--u1 matches code vars then-rest)
(pcase--u else-rest))))
- (t (error "Unkown QPattern %s" qpat))))
+ (t (error "Unknown QPattern %s" qpat))))
(provide 'pcase)
HCoop / bpt / emacs.git / blobdiff