(and UPAT...) matches if all the patterns match.
'VAL matches if the object is `equal' to VAL
`QPAT matches if the QPattern QPAT matches.
- (pred PRED) matches if PRED applied to the object returns non-nil.
+ (pred FUN) matches if FUN applied to the object returns non-nil.
(guard BOOLEXP) matches if BOOLEXP evaluates to non-nil.
(let UPAT EXP) matches if EXP matches UPAT.
(app FUN UPAT) matches if FUN applied to the object 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.
-FUN can be either of the form (lambda ARGS BODY) or a symbol.
-It has to obey the rule that if (FUN X) returns V then calling it again will
-return the same V again (so that multiple (FUN X) can be consolidated).
-
QPatterns can take the following forms:
(QPAT1 . QPAT2) matches if QPAT1 matches the car and QPAT2 the cdr.
[QPAT1 QPAT2..QPATn] matches a vector of length n and QPAT1..QPATn match
STRING matches if the object is `equal' to STRING.
ATOM matches if the object is `eq' to ATOM.
-PRED can take the form
- FUNCTION in which case it gets called with one argument.
+FUN can take the form
+ SYMBOL or (lambda ARGS BODY) in which case it's called with one argument.
(F ARG1 .. ARGn) in which case F 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.
+So a FUN of the form SYMBOL is equivalent to one of the form (FUN).
+FUN can refer to variables bound earlier in the pattern.
+FUN is assumed to be pure, i.e. it can be dropped if its result is not used,
+and two identical calls can be merged into one.
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 (debug (sexp body)))
`(,fun ,arg2 ,arg1))
+(defun pcase--funcall (fun arg vars)
+ "Build a function call to FUN with arg ARG."
+ (if (symbolp fun)
+ `(,fun ,arg)
+ (let* (;; `vs' is an upper bound on the vars we need.
+ (vs (pcase--fgrep (mapcar #'car vars) fun))
+ (env (mapcar (lambda (var)
+ (list var (cdr (assq var vars))))
+ vs))
+ (call (progn
+ (when (memq arg vs)
+ ;; `arg' is shadowed by `env'.
+ (let ((newsym (make-symbol "x")))
+ (push (list newsym arg) env)
+ (setq arg newsym)))
+ (if (functionp fun)
+ `(funcall #',fun ,arg)
+ `(,@fun ,arg)))))
+ (if (null vs)
+ call
+ ;; Let's not replace `vars' in `fun' since it's
+ ;; too difficult to do it right, instead just
+ ;; let-bind `vars' around `fun'.
+ `(let* ,env ,call)))))
+
+(defun pcase--eval (exp vars)
+ "Build an expression that will evaluate EXP."
+ (let* ((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)))))
+
;; It's very tempting to use `pcase' below, tho obviously, it'd create
;; bootstrapping problems.
(defun pcase--u1 (matches code vars rest)
sym (lambda (pat) (pcase--split-pred vars upat pat)) 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))
- (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)
- `(funcall #',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* ,env ,call))))
+ (pcase--if (if (eq (car upat) 'pred)
+ (pcase--funcall (cadr upat) sym vars)
+ (pcase--eval (cadr upat) vars))
(pcase--u1 matches code vars then-rest)
(pcase--u else-rest))))
((symbolp upat)
;; (cons (cons (nth 1 upat) (nth 2 upat)) vars) rest)
(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--eval (nth 2 upat) vars)
(pcase--u1 (cons (pcase--match sym (nth 1 upat)) matches)
code vars rest)))
((eq (car-safe upat) 'app)
(if (not (get nsym 'pcase-used))
body
(macroexp-let*
- `((,nsym
- ,(if (symbolp fun)
- `(,fun ,sym)
- (let* ((vs (pcase--fgrep (mapcar #'car vars) fun))
- (env (mapcar (lambda (v) (list v (cdr (assq v vars))))
- vs))
- (call `(funcall #',fun ,sym)))
- (if env (macroexp-let* env call) call)))))
+ `((,nsym ,(pcase--funcall fun sym vars)))
body))))
((eq (car-safe upat) 'quote)
(pcase--mark-used sym)
(app length ,(length qpat))
,@(let ((upats nil))
(dotimes (i (length qpat))
- (push `(app (lambda (v) (aref v ,i)) ,(list '\` (aref qpat i)))
+ (push `(app (pcase--flip aref ,i) ,(list '\` (aref qpat i)))
upats))
(nreverse upats))))
((consp qpat)
projects / emacs.git / commitdiff