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-rw-r--r--lisp/emacs-lisp/pcase.el349
1 files changed, 205 insertions, 144 deletions
diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
index afbc5df85ce..4aeed7e4d0e 100644
--- a/lisp/emacs-lisp/pcase.el
+++ b/lisp/emacs-lisp/pcase.el
@@ -1,4 +1,4 @@
-;;; pcase.el --- ML-style pattern-matching macro for Elisp -*- lexical-binding: t -*-
+;;; pcase.el --- ML-style pattern-matching macro for Elisp -*- lexical-binding: t; coding: utf-8 -*-
;; Copyright (C) 2010-2012 Free Software Foundation, Inc.
@@ -39,25 +39,53 @@
;; - 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.
+;; - provide a way to fallthrough to subsequent cases (not sure what I meant by
+;; this :-()
;; - 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).
+;; to be performed anyway, so better do it first so it's shared).
;; - then choose the test that discriminates more (?).
+;; - provide Agda's `with' (along with its `...' companion).
+;; - implement (not UPAT). This might require a significant redesign.
;; - 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:
+(require 'macroexp)
+
;; 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 'key :test 'eq))
-
-(defconst pcase--dontcare-upats '(t _ dontcare))
+;; (defconst pcase--memoize-1 (make-hash-table :test 'eq))
+;; (defconst pcase--memoize-2 (make-hash-table :weakness 'key :test 'equal))
+
+(defconst pcase--dontcare-upats '(t _ pcase--dontcare))
+
+(def-edebug-spec
+ pcase-UPAT
+ (&or symbolp
+ ("or" &rest pcase-UPAT)
+ ("and" &rest pcase-UPAT)
+ ("`" pcase-QPAT)
+ ("guard" form)
+ ("let" pcase-UPAT form)
+ ("pred"
+ &or lambda-expr
+ ;; Punt on macros/special forms.
+ (functionp &rest form)
+ sexp)
+ sexp))
+
+(def-edebug-spec
+ pcase-QPAT
+ (&or ("," pcase-UPAT)
+ (pcase-QPAT . pcase-QPAT)
+ sexp))
;;;###autoload
(defmacro pcase (exp &rest cases)
@@ -66,6 +94,7 @@ CASES is a list of elements of the form (UPATTERN CODE...).
UPatterns can take the following forms:
_ matches anything.
+ SELFQUOTING matches itself. This includes keywords, numbers, and strings.
SYMBOL matches anything and binds it to SYMBOL.
(or UPAT...) matches if any of the patterns matches.
(and UPAT...) matches if all the patterns match.
@@ -85,13 +114,14 @@ QPatterns for vectors are not implemented yet.
PRED can take the form
FUNCTION in which case it gets called with one argument.
- (FUN ARG1 .. ARGN) in which case it gets called with N+1 arguments.
+ (FUN ARG1 .. ARGN) in which case it gets called with an N+1'th argument
+ which is the value being matched.
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.
E.g. you can match pairs where the cdr is larger than the car with a 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.
+ (declare (indent 1) (debug (form &rest (pcase-UPAT body))))
;; 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
@@ -102,37 +132,57 @@ like `(,a . ,(pred (< a))) or, with more checks:
(if (and (equal exp (car data)) (equal cases (cadr data)))
;; We have the right expansion.
(cddr data)
+ ;; (when (gethash (car cases) pcase--memoize-1)
+ ;; (message "pcase-memoize failed because of weak key!!"))
+ ;; (when (gethash (car cases) pcase--memoize-2)
+ ;; (message "pcase-memoize failed because of eq test on %S"
+ ;; (car cases)))
(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)
+ (puthash (car cases) `(,exp ,cases ,@expansion) pcase--memoize)
+ ;; (puthash (car cases) `(,exp ,cases ,@expansion) pcase--memoize-1)
+ ;; (puthash (car cases) `(,exp ,cases ,@expansion) pcase--memoize-2)
expansion))))
+(defun pcase--let* (bindings body)
+ (cond
+ ((null bindings) (macroexp-progn body))
+ ((pcase--trivial-upat-p (caar bindings))
+ (macroexp-let* `(,(car bindings)) (pcase--let* (cdr bindings) body)))
+ (t
+ (let ((binding (pop bindings)))
+ (pcase--expand
+ (cadr binding)
+ `((,(car binding) ,(pcase--let* bindings body))
+ ;; We can either signal an error here, or just use `pcase--dontcare'
+ ;; which generates more efficient code. In practice, if we use
+ ;; `pcase--dontcare' we will still often get an error and the few
+ ;; cases where we don't do not matter that much, so
+ ;; it's a better choice.
+ (pcase--dontcare nil)))))))
+
;;;###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))
- (cond
- ((null bindings) (if (> (length body) 1) `(progn ,@body) (car body)))
- ((pcase--trivial-upat-p (caar bindings))
- `(let (,(car bindings)) (pcase-let* ,(cdr bindings) ,@body)))
- (t
- `(pcase ,(cadr (car bindings))
- (,(caar bindings) (pcase-let* ,(cdr bindings) ,@body))
- ;; We can either signal an error here, or just use `dontcare' which
- ;; generates more efficient code. In practice, if we use `dontcare' we
- ;; will still often get an error and the few cases where we don't do not
- ;; matter that much, so it's a better choice.
- (dontcare nil)))))
+ (declare (indent 1)
+ (debug ((&rest (pcase-UPAT &optional form)) body)))
+ (let ((cached (gethash bindings pcase--memoize)))
+ ;; cached = (BODY . EXPANSION)
+ (if (equal (car cached) body)
+ (cdr cached)
+ (let ((expansion (pcase--let* bindings body)))
+ (puthash bindings (cons body 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 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 '()))
@@ -148,6 +198,7 @@ of the form (UPAT EXP)."
`(let ,(nreverse bindings) (pcase-let* ,matches ,@body)))))
(defmacro pcase-dolist (spec &rest body)
+ (declare (indent 1) (debug ((pcase-UPAT form) body)))
(if (pcase--trivial-upat-p (car spec))
`(dolist ,spec ,@body)
(let ((tmpvar (make-symbol "x")))
@@ -162,64 +213,78 @@ of the form (UPAT EXP)."
(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)))))
- (seen '())
- (codegen
- (lambda (code vars)
- (let ((prev (assq code seen)))
- (if (not prev)
- (let ((res (pcase-codegen code vars)))
- (push (list code vars res) seen)
- res)
- ;; Since we use a tree-based pattern matching
- ;; technique, the leaves (the places that contain the
- ;; code to run once a pattern is matched) can get
- ;; copied a very large number of times, so to avoid
- ;; code explosion, we need to keep track of how many
- ;; times we've used each leaf and move it
- ;; to a separate function if that number is too high.
- ;;
- ;; We've already used this branch. So it is shared.
- (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.
- (let ((bsym
- (make-symbol (format "pcase-%d" (length defs)))))
- (push `(,bsym (lambda ,(mapcar #'car prevvars) ,@code)) defs)
- (setcar res 'funcall)
- (setcdr res (cons bsym (mapcar #'cdr prevvars)))
- (setcar (cddr prev) bsym)
- (setq res bsym)))
- (setq vars (copy-sequence vars))
- (let ((args (mapcar (lambda (pa)
- (let ((v (assq (car pa) vars)))
- (setq vars (delq v vars))
- (cdr v)))
- prevvars)))
- (when vars ;New additional vars.
- (error "The vars %s are only bound in some paths"
- (mapcar #'car vars)))
- `(funcall ,res ,@args)))))))
- (main
- (pcase--u
- (mapcar (lambda (case)
- `((match ,exp . ,(car case))
- ,(apply-partially
- (if (pcase--small-branch-p (cdr case))
- ;; Don't bother sharing multiple
- ;; occurrences of this leaf since it's small.
- #'pcase-codegen codegen)
- (cdr case))))
- cases))))
- (if (null defs) main
- `(let ,defs ,main))))
+ (macroexp-let2 macroexp-copyable-p val exp
+ (let* ((defs ())
+ (seen '())
+ (codegen
+ (lambda (code vars)
+ (let ((prev (assq code seen)))
+ (if (not prev)
+ (let ((res (pcase-codegen code vars)))
+ (push (list code vars res) seen)
+ res)
+ ;; Since we use a tree-based pattern matching
+ ;; technique, the leaves (the places that contain the
+ ;; code to run once a pattern is matched) can get
+ ;; copied a very large number of times, so to avoid
+ ;; code explosion, we need to keep track of how many
+ ;; times we've used each leaf and move it
+ ;; to a separate function if that number is too high.
+ ;;
+ ;; We've already used this branch. So it is shared.
+ (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.
+ (let ((bsym
+ (make-symbol (format "pcase-%d" (length defs)))))
+ (push `(,bsym (lambda ,(mapcar #'car prevvars) ,@code))
+ defs)
+ (setcar res 'funcall)
+ (setcdr res (cons bsym (mapcar #'cdr prevvars)))
+ (setcar (cddr prev) bsym)
+ (setq res bsym)))
+ (setq vars (copy-sequence vars))
+ (let ((args (mapcar (lambda (pa)
+ (let ((v (assq (car pa) vars)))
+ (setq vars (delq v vars))
+ (cdr v)))
+ prevvars)))
+ ;; If some of `vars' were not found in `prevvars', that's
+ ;; OK it just means those vars aren't present in all
+ ;; branches, so they can be used within the pattern
+ ;; (e.g. by a `guard/let/pred') but not in the branch.
+ ;; FIXME: But if some of `prevvars' are not in `vars' we
+ ;; should remove them from `prevvars'!
+ `(funcall ,res ,@args)))))))
+ (used-cases ())
+ (main
+ (pcase--u
+ (mapcar (lambda (case)
+ `((match ,val . ,(car case))
+ ,(lambda (vars)
+ (unless (memq case used-cases)
+ ;; Keep track of the cases that are used.
+ (push case used-cases))
+ (funcall
+ (if (pcase--small-branch-p (cdr case))
+ ;; Don't bother sharing multiple
+ ;; occurrences of this leaf since it's small.
+ #'pcase-codegen codegen)
+ (cdr case)
+ vars))))
+ cases))))
+ (dolist (case cases)
+ (unless (or (memq case used-cases) (eq (car case) 'pcase--dontcare))
+ (message "Redundant pcase pattern: %S" (car case))))
+ (macroexp-let* defs main))))
(defun pcase-codegen (code vars)
+ ;; Don't use let*, otherwise macroexp-let* may merge it with some surrounding
+ ;; let* which might prevent the setcar/setcdr in pcase--expand's fancy
+ ;; codegen from later metamorphosing this let into a funcall.
`(let ,(mapcar (lambda (b) (list (car b) (cdr b))) vars)
,@code))
@@ -237,23 +302,7 @@ of the form (UPAT EXP)."
(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.
- ;; FIXME: ideally, this should never happen because the pcase--split-*
- ;; funs should have eliminated such things, but pcase--split-member
- ;; is imprecise, so in practice it can happen occasionally.
- `(if ,test ,then ,@(nthcdr 3 else))
- `(cond (,test ,then)
- (,(nth 1 else) ,(nth 2 else))
- (t ,@(nthcdr 3 else)))))
- ((eq (car-safe else) 'cond)
- `(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))))
+ (t (macroexp-if test then else))))
(defun pcase--upat (qpattern)
(cond
@@ -433,26 +482,26 @@ MATCH is the pattern that needs to be matched, of the form:
(defun pcase--split-pred (upat pat)
;; FIXME: For predicates like (pred (> a)), two such predicates may
;; actually refer to different variables `a'.
- (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)
- ;; (progn (message "Trying predicate %S" (cadr upat))
- ;; (ignore-errors
- ;; (funcall (cadr upat) (cadr pat)))))
- ;; (message "Simplify pred %S against %S" upat pat)
- ;; (cons nil :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."
@@ -463,6 +512,9 @@ MATCH is the pattern that needs to be matched, of the form:
(and (memq sexp vars) (not (memq sexp res)) (push sexp res))
res))
+(defun pcase--self-quoting-p (upat)
+ (or (keywordp upat) (numberp upat) (stringp upat)))
+
;; It's very tempting to use `pcase' below, tho obviously, it'd create
;; bootstrapping problems.
(defun pcase--u1 (matches code vars rest)
@@ -525,12 +577,12 @@ Otherwise, it defers to REST which is a list of branches of the form
(upat (cdr cdrpopmatches)))
(cond
((memq upat '(t _)) (pcase--u1 matches code vars rest))
- ((eq upat 'dontcare) :pcase--dontcare)
+ ((eq upat 'pcase--dontcare) :pcase--dontcare)
((memq (car-safe upat) '(guard pred))
(if (eq (car upat) 'pred) (put sym 'pcase-used t))
(let* ((splitrest
(pcase--split-rest
- sym (apply-partially #'pcase--split-pred upat) rest))
+ sym (lambda (pat) (pcase--split-pred upat pat)) rest))
(then-rest (car splitrest))
(else-rest (cdr splitrest)))
(pcase--if (if (and (eq (car upat) 'pred) (symbolp (cadr upat)))
@@ -548,7 +600,8 @@ Otherwise, it defers to REST which is a list of branches of the form
(let ((newsym (make-symbol "x")))
(push (list newsym sym) env)
(setq sym newsym)))
- (if (functionp exp) `(,exp ,sym)
+ (if (functionp exp)
+ `(funcall #',exp ,sym)
`(,@exp ,sym)))))
(if (null vs)
call
@@ -558,6 +611,9 @@ Otherwise, it defers to REST which is a list of branches of the form
`(let* ,env ,call))))
(pcase--u1 matches code vars then-rest)
(pcase--u else-rest))))
+ ((pcase--self-quoting-p upat)
+ (put sym 'pcase-used t)
+ (pcase--q1 sym upat matches code vars rest))
((symbolp upat)
(put sym 'pcase-used t)
(if (not (assq upat vars))
@@ -570,21 +626,17 @@ Otherwise, it defers to REST which is a list of branches of the form
;; 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))))
+ (macroexp-let2
+ macroexp-copyable-p sym
+ (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 (macroexp-let* env exp) exp))))
+ (pcase--u1 (cons `(match ,sym . ,(nth 1 upat)) matches)
+ code vars rest)))
((eq (car-safe upat) '\`)
(put sym 'pcase-used t)
(pcase--q1 sym (cadr upat) matches code vars rest))
@@ -593,19 +645,22 @@ Otherwise, it defers to REST which is a list of branches of the form
(memq-fine t))
(when all
(dolist (alt (cdr upat))
- (unless (and (eq (car-safe alt) '\`)
- (or (symbolp (cadr alt)) (integerp (cadr alt))
- (setq memq-fine nil)
- (stringp (cadr alt))))
+ (unless (or (pcase--self-quoting-p alt)
+ (and (eq (car-safe alt) '\`)
+ (or (symbolp (cadr alt)) (integerp (cadr alt))
+ (setq memq-fine nil)
+ (stringp (cadr alt)))))
(setq all nil))))
(if all
;; Use memq for (or `a `b `c `d) rather than a big tree.
- (let* ((elems (mapcar 'cadr (cdr upat)))
+ (let* ((elems (mapcar (lambda (x) (if (consp x) (cadr x) x))
+ (cdr upat)))
(splitrest
(pcase--split-rest
- sym (apply-partially #'pcase--split-member elems) rest))
+ sym (lambda (pat) (pcase--split-member elems pat)) rest))
(then-rest (car splitrest))
(else-rest (cdr splitrest)))
+ (put sym 'pcase-used t)
(pcase--if `(,(if memq-fine #'memq #'member) ,sym ',elems)
(pcase--u1 matches code vars then-rest)
(pcase--u else-rest)))
@@ -659,7 +714,7 @@ Otherwise, it defers to REST which is a list of branches of the form
(symd (make-symbol "xcdr"))
(splitrest (pcase--split-rest
sym
- (apply-partially #'pcase--split-consp syma symd)
+ (lambda (pat) (pcase--split-consp syma symd pat))
rest))
(then-rest (car splitrest))
(else-rest (cdr splitrest))
@@ -673,16 +728,22 @@ Otherwise, it defers to REST which is a list of branches of the form
;; 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.
- `(let (,@(if (get syma 'pcase-used) `((,syma (car ,sym))))
+ ;; FIXME: Some of those let bindings occur too early (they are used in
+ ;; `then-body', but only within some sub-branch).
+ (macroexp-let*
+ `(,@(if (get syma 'pcase-used) `((,syma (car ,sym))))
,@(if (get symd 'pcase-used) `((,symd (cdr ,sym)))))
- ,then-body)
+ then-body)
(pcase--u else-rest))))
((or (integerp qpat) (symbolp qpat) (stringp qpat))
(let* ((splitrest (pcase--split-rest
- sym (apply-partially 'pcase--split-equal qpat) rest))
+ sym (lambda (pat) (pcase--split-equal qpat pat)) rest))
(then-rest (car splitrest))
(else-rest (cdr splitrest)))
- (pcase--if `(,(if (stringp qpat) #'equal #'eq) ,sym ',qpat)
+ (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 "Unknown QPattern %s" qpat))))
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