From: Michael Heerdegen <michael_heerdegen@web.de>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: Nicolas Petton <nicolas@petton.fr>, Eli Zaretskii <eliz@gnu.org>,
Emacs Development <emacs-devel@gnu.org>
Subject: Re: `thunk-let'?
Date: Wed, 22 Nov 2017 03:50:47 +0100 [thread overview]
Message-ID: <87h8tnowl4.fsf@web.de> (raw)
In-Reply-To: <jwvvaij47cv.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Thu, 09 Nov 2017 13:48:43 -0500")
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Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
> Yeah, pretty ugly. Now I see why my intuition told me that lazy-let
> should be in thunk.el ;-)
Ok, I updated the patch accordingly (attached): the stuff goes to
thunk.el now, I added a note to the file header, renamed everything,
added some more details to the docstrings, moved the tests, and removed
the "---" from the News entry.
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From 250b999e094ccdf11e37bb80f2d6a41b64b96dfd Mon Sep 17 00:00:00 2001
From: Michael Heerdegen <michael_heerdegen@web.de>
Date: Thu, 2 Nov 2017 18:45:34 +0100
Subject: [PATCH] Add macros `thunk-let' and `thunk-let*'
* lisp/emacs-lisp/thunk.el (thunk-let, thunk-let*): New macros.
* test/lisp/emacs-lisp/thunk-tests.el:
(thunk-let-basic-test, thunk-let*-basic-test)
(thunk-let-bound-vars-cant-be-set-test)
(thunk-let-laziness-test, thunk-let*-laziness-test)
(thunk-let-bad-binding-test): New tests for `thunk-let' and
`thunk-let*.
---
etc/NEWS | 4 +++
lisp/emacs-lisp/thunk.el | 56 +++++++++++++++++++++++++++++++++++++
test/lisp/emacs-lisp/thunk-tests.el | 50 +++++++++++++++++++++++++++++++++
3 files changed, 110 insertions(+)
diff --git a/etc/NEWS b/etc/NEWS
index c47ca42d27..bfa8be39f9 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -109,6 +109,10 @@ Snake and Pong are more playable on HiDPI displays.
*** Completing filenames in the minibuffer via 'C-TAB' now uses the
styles as configured by the variable 'completion-styles'.
+** Thunk
+*** The new macros 'thunk-let' and 'thunk-let*' are analogue to `let'
+and `let*' but create bindings that are evaluated lazily.
+
\f
* New Modes and Packages in Emacs 27.1
diff --git a/lisp/emacs-lisp/thunk.el b/lisp/emacs-lisp/thunk.el
index 371d10444b..9cb16857f4 100644
--- a/lisp/emacs-lisp/thunk.el
+++ b/lisp/emacs-lisp/thunk.el
@@ -41,6 +41,10 @@
;; following:
;;
;; (thunk-force delayed)
+;;
+;; This file also defines macros `thunk-let' and `thunk-let*' that are
+;; analogous to `let' and `let*' but provide lazy evaluation of
+;; bindings by using thunks implicitly (i.e. in the expansion).
;;; Code:
@@ -71,5 +75,57 @@ thunk-evaluated-p
"Return non-nil if DELAYED has been evaluated."
(funcall delayed t))
+(defmacro thunk-let (bindings &rest body)
+ "Like `let' but create lazy bindings.
+
+BINDINGS is a list of elements of the form (SYMBOL EXPRESSION).
+Any binding EXPRESSION is not evaluated before the variable
+SYMBOL is used for the first time when evaluating the BODY.
+
+It is not allowed to set `thunk-let' or `thunk-let*' bound
+variables.
+
+Using `thunk-let' and `thunk-let*' requires `lexical-binding'."
+ (declare (indent 1) (debug let))
+ (cl-callf2 mapcar
+ (lambda (binding)
+ (pcase binding
+ (`(,(pred symbolp) ,_) binding)
+ (_ (signal 'error (cons "Bad binding in thunk-let"
+ (list binding))))))
+ bindings)
+ (cl-callf2 mapcar
+ (pcase-lambda (`(,var ,binding))
+ (list (make-symbol (concat (symbol-name var) "-thunk"))
+ var binding))
+ bindings)
+ `(let ,(mapcar
+ (pcase-lambda (`(,thunk-var ,_var ,binding))
+ `(,thunk-var (thunk-delay ,binding)))
+ bindings)
+ (cl-symbol-macrolet
+ ,(mapcar (pcase-lambda (`(,thunk-var ,var ,_binding))
+ `(,var (thunk-force ,thunk-var)))
+ bindings)
+ ,@body)))
+
+(defmacro thunk-let* (bindings &rest body)
+ "Like `let*' but create lazy bindings.
+
+BINDINGS is a list of elements of the form (SYMBOL EXPRESSION).
+Any binding EXPRESSION is not evaluated before the variable
+SYMBOL is used for the first time when evaluating the BODY.
+
+It is not allowed to set `thunk-let' or `thunk-let*' bound
+variables.
+
+Using `thunk-let' and `thunk-let*' requires `lexical-binding'."
+ (declare (indent 1) (debug let))
+ (cl-reduce
+ (lambda (expr binding) `(thunk-let (,binding) ,expr))
+ (nreverse bindings)
+ :initial-value (macroexp-progn body)))
+
+
(provide 'thunk)
;;; thunk.el ends here
diff --git a/test/lisp/emacs-lisp/thunk-tests.el b/test/lisp/emacs-lisp/thunk-tests.el
index 973a14b818..e122098b16 100644
--- a/test/lisp/emacs-lisp/thunk-tests.el
+++ b/test/lisp/emacs-lisp/thunk-tests.el
@@ -51,5 +51,55 @@
(thunk-force thunk)
(should (= x 1))))
+
+\f
+;; thunk-let tests
+
+(ert-deftest thunk-let-basic-test ()
+ "Test whether bindings are established."
+ (should (equal (thunk-let ((x 1) (y 2)) (+ x y)) 3)))
+
+(ert-deftest thunk-let*-basic-test ()
+ "Test whether bindings are established."
+ (should (equal (thunk-let* ((x 1) (y (+ 1 x))) (+ x y)) 3)))
+
+(ert-deftest thunk-let-bound-vars-cant-be-set-test ()
+ "Test whether setting a `thunk-let' bound variable fails."
+ (should-error
+ (eval '(thunk-let ((x 1)) (let ((y 7)) (setq x (+ x y)) (* 10 x))) t)))
+
+(ert-deftest thunk-let-laziness-test ()
+ "Test laziness of `thunk-let'."
+ (should
+ (equal (let ((x-evalled nil)
+ (y-evalled nil))
+ (thunk-let ((x (progn (setq x-evalled t) (+ 1 2)))
+ (y (progn (setq y-evalled t) (+ 3 4))))
+ (let ((evalled-y y))
+ (list x-evalled y-evalled evalled-y))))
+ (list nil t 7))))
+
+(ert-deftest thunk-let*-laziness-test ()
+ "Test laziness of `thunk-let*'."
+ (should
+ (equal (let ((x-evalled nil)
+ (y-evalled nil)
+ (z-evalled nil)
+ (a-evalled nil))
+ (thunk-let* ((x (progn (setq x-evalled t) (+ 1 1)))
+ (y (progn (setq y-evalled t) (+ x 1)))
+ (z (progn (setq z-evalled t) (+ y 1)))
+ (a (progn (setq a-evalled t) (+ z 1))))
+ (let ((evalled-z z))
+ (list x-evalled y-evalled z-evalled a-evalled evalled-z))))
+ (list t t t nil 4))))
+
+(ert-deftest thunk-let-bad-binding-test ()
+ "Test whether a bad binding causes a compiler error."
+ (should-error (byte-compile (thunk-let ((x 1 1)) x)))
+ (should-error (byte-compile (thunk-let (27) x)))
+ (should-error (byte-compile (thunk-let x x))))
+
+
(provide 'thunk-tests)
;;; thunk-tests.el ends here
--
2.15.0
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Is this ok to install now?
@Eli: I think we can still add the words I wrote to the manual. What is
the cheapest way to learn enough of texinfo and its usage by the Emacs
manual to be able to create a correct patch?
Thanks,
Michael.
next prev parent reply other threads:[~2017-11-22 2:50 UTC|newest]
Thread overview: 77+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-08 20:12 `thunk-let'? Michael Heerdegen
2017-10-08 22:25 ` `thunk-let'? Michael Heerdegen
2017-10-09 3:10 ` `thunk-let'? Stefan Monnier
2017-10-09 11:40 ` `thunk-let'? Michael Heerdegen
2017-10-09 14:07 ` `thunk-let'? Michael Heerdegen
2017-10-09 14:27 ` `thunk-let'? Michael Heerdegen
2017-10-09 15:38 ` [SUSPECTED SPAM] `thunk-let'? Stefan Monnier
2017-11-08 17:22 ` Michael Heerdegen
2017-11-08 18:02 ` Stefan Monnier
2017-11-09 15:14 ` Michael Heerdegen
2017-11-09 18:39 ` `thunk-let'? Michael Heerdegen
2017-11-09 18:48 ` `thunk-let'? Stefan Monnier
2017-11-22 2:50 ` Michael Heerdegen [this message]
2017-11-22 3:43 ` `thunk-let'? Eli Zaretskii
2017-11-22 16:16 ` `thunk-let'? Eli Zaretskii
2017-11-22 19:25 ` `thunk-let'? Michael Heerdegen
2017-11-22 20:00 ` `thunk-let'? Eli Zaretskii
2017-11-23 2:59 ` `thunk-let'? Michael Heerdegen
2017-11-23 4:15 ` `thunk-let'? Michael Heerdegen
2017-11-23 16:34 ` `thunk-let'? Pip Cet
2017-11-23 23:41 ` `thunk-let'? Michael Heerdegen
2017-11-24 8:37 ` `thunk-let'? Eli Zaretskii
2017-11-24 8:51 ` `thunk-let'? Stefan Monnier
2017-11-24 9:16 ` `thunk-let'? Eli Zaretskii
2017-11-24 13:33 ` `thunk-let'? Stefan Monnier
2017-11-27 5:21 ` `thunk-let'? Michael Heerdegen
2017-11-27 13:34 ` `thunk-let'? Stefan Monnier
2017-11-27 15:44 ` `thunk-let'? Eli Zaretskii
2017-11-30 15:19 ` `thunk-let'? Michael Heerdegen
2017-11-24 8:36 ` `thunk-let'? Eli Zaretskii
2017-11-30 15:17 ` `thunk-let'? Michael Heerdegen
2017-11-30 16:06 ` `thunk-let'? Eli Zaretskii
2017-12-01 8:02 ` `thunk-let'? Michael Heerdegen
2017-11-23 16:04 ` `thunk-let'? Eli Zaretskii
2017-11-22 17:44 ` `thunk-let'? Gemini Lasswell
2017-11-22 18:04 ` `thunk-let'? Noam Postavsky
2017-11-22 18:31 ` `thunk-let'? Michael Heerdegen
2017-11-22 18:29 ` `thunk-let'? Michael Heerdegen
2017-11-22 19:54 ` `thunk-let'? Stefan Monnier
2017-11-22 22:47 ` `thunk-let'? Michael Heerdegen
2017-11-10 10:01 ` [SUSPECTED SPAM] `thunk-let'? Eli Zaretskii
2017-11-08 18:04 ` Eli Zaretskii
2017-11-08 22:22 ` `thunk-let'? Michael Heerdegen
2017-11-08 23:06 ` `thunk-let'? Drew Adams
2017-11-09 17:20 ` `thunk-let'? Eli Zaretskii
2017-11-09 17:39 ` `thunk-let'? Clément Pit-Claudel
2017-11-09 18:06 ` `thunk-let'? Michael Heerdegen
2017-11-09 21:05 ` `thunk-let'? Drew Adams
2017-11-09 23:07 ` Sandbox subr-x? (was: `thunk-let'?) Michael Heerdegen
2017-11-09 23:54 ` Drew Adams
2017-11-10 7:57 ` Eli Zaretskii
2017-11-09 21:48 ` `thunk-let'? Clément Pit-Claudel
2017-11-09 22:43 ` `thunk-let'? Michael Heerdegen
2017-11-10 7:48 ` `thunk-let'? Eli Zaretskii
2017-11-09 18:14 ` `thunk-let'? Michael Heerdegen
2017-11-09 20:26 ` `thunk-let'? Eli Zaretskii
2017-11-09 23:13 ` `thunk-let'? Michael Heerdegen
2017-11-10 7:58 ` `thunk-let'? Eli Zaretskii
2017-11-11 15:20 ` `thunk-let'? Michael Heerdegen
2017-11-11 15:40 ` `thunk-let'? Eli Zaretskii
2017-11-10 10:10 ` `thunk-let'? Nicolas Petton
2017-11-09 14:34 ` [SUSPECTED SPAM] `thunk-let'? Michael Heerdegen
2017-11-09 17:12 ` Eli Zaretskii
2017-11-09 15:19 ` Michael Heerdegen
2017-10-09 8:00 ` `thunk-let'? Nicolas Petton
2017-12-08 20:38 ` A generalization of `thunk-let' (was: `thunk-let'?) Michael Heerdegen
2017-12-08 21:16 ` A generalization of `thunk-let' Stefan Monnier
2017-12-09 10:33 ` Michael Heerdegen
2017-12-10 4:47 ` Stefan Monnier
2017-12-10 5:34 ` John Wiegley
2017-12-12 14:41 ` Michael Heerdegen
2017-12-13 13:52 ` Michael Heerdegen
2017-12-13 14:09 ` Stefan Monnier
2017-12-13 14:37 ` Michael Heerdegen
2018-01-12 20:03 ` Michael Heerdegen
2017-12-09 21:59 ` A generalization of `thunk-let' (was: `thunk-let'?) Richard Stallman
2017-12-10 17:03 ` A generalization of `thunk-let' Michael Heerdegen
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