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(pcase): New _ syntax in pred/app functions

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The current syntax for functions in `app` and `pred` patterns
allows a shorthand (F ARGS) where the object being matched is
added as an extra last argument.  This is nice for things like
(pred (< 5)) but sometimes the object needs to be at
another position.
Until now you had to use (pred (lambda (x) (memq x my-list)))
or (pred (pcase--flip memq my-list)) in those cases.
So, introduce a new shorthand where `_` can be used to indicate
where the object should be passed: (pred (memq _ my-list))

* lisp/emacs-lisp/pcase.el (pcase--split-pred): Document new syntax
for pred/app functions.
(pcase--funcall): Support new syntax.
(pcase--flip): Declare obsolete.
(pcase--u1, \`): Use `_` instead.
(pcase--split-pred): Adjust accordingly.

* doc/lispref/control.texi (pcase Macro): Document new syntax
for pred/app functions.

* lisp/progmodes/opascal.el (pcase-defmacro):
* lisp/emacs-lisp/seq.el (seq--make-pcase-bindings):
* lisp/emacs-lisp/eieio.el (eieio):
* lisp/emacs-lisp/cl-macs.el (cl-struct, cl-type):
Use _ instead of `pcase--flip`.
(cl--pcase-mutually-exclusive-p): Adjust accordingly.

* lisp/emacs-lisp/map.el (map--pcase-map-elt): Declare obsolete.
(map--make-pcase-bindings): Use `_` instead.
This commit is contained in:
Stefan Monnier 2024-02-11 22:00:44 -05:00
parent 9ebc91795f
commit 806759dc0a
8 changed files with 47 additions and 24 deletions
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4
lisp/emacs-lisp/seq.el
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@ -619,12 +619,12 @@ SEQUENCE must be a sequence of numbers or markers."
(unless rest-marker
(pcase name
(`&rest
(progn (push `(app (pcase--flip seq-drop ,index)
(progn (push `(app (seq-drop _ ,index)
,(seq--elt-safe args (1+ index)))
bindings)
(setq rest-marker t)))
(_
(push `(app (pcase--flip seq--elt-safe ,index) ,name) bindings))))
(push `(app (seq--elt-safe _ ,index) ,name) bindings))))
(setq index (1+ index)))
bindings))