From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: arthur miller Newsgroups: gmane.emacs.devel Subject: Sv: Is this a bug in while-let or do I missunderstand it? Date: Sun, 10 Nov 2024 19:49:00 +0000 Message-ID: References: <86ldxrliau.fsf@gnu.org> <86ttcfv0bc.fsf@fastmail.fm> Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="_000_DU2PR02MB10109373D5E48CFFBD2618000965F2DU2PR02MB10109eu_" Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="39320"; mail-complaints-to="usenet@ciao.gmane.io" Cc: "eliz@gnu.org" , "yuri.v.khan@gmail.com" , "emacs-devel@gnu.org" To: "Alfred M. 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:325388 Archived-At: --_000_DU2PR02MB10109373D5E48CFFBD2618000965F2DU2PR02MB10109eu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable > @defmac while-let spec then-forms... > Like @code{when-let*}, but repeat until a binding in @var{spec} is > @code{nil}. The return value is always @code{nil}. > >The "Like FOO" is confusing -- it is not like when-let*, when-let* is >also not like let*. E.g., when spec is (binding value) or just >(value) (!?) -- which should be mentioned in the manual. > >These foo-LET are are mixing up the condition being tested and the >binding, when there is no binding the form seems to be just a test as >if you'd pass it directly to WHEN (or whatever). There should be some >example that SPEC is not at all like in LET, and that: > >(when-let* ((result1 (do-computation)) > ( (do-more result1))) > (do-something result1)) > >is something like (I guess?): > >(let ((result1 (do-computation))) > (when result1 > (when (do-more result1) > (do-something result2)))) > >And these mentions of "Like LET*" should be removed entierly. > >But this is a better, and a good start. > > @code{while-let} replaces a common pattern in which a binding is > established outside the @{while}-loop, tested as part of the condition = of > @{while} and subsequently changed inside the loop using the same expres= sion > that it was originally bound to: > > @example > (let ((result (do-computation))) > (while result > (do-stuff-with result) > (setq result (do-computation)))) > @end example > > Using @code{while-let}, this can be written more succinctly as: > > @example > (while-let ((result (do-computation))) > (do-stuff-with result)) > @end example > > The binding of @code{result} is reestablished at every iteration, there= fore > setting the value of @code{result} inside the loop has no effect. In or= der > to end the loop, @code{(do-computation)} should eventually return > @code{nil}. > > This example uses a single binding for clarity, but obviously > @code{while-let} can establish multiple bindings. The loop runs as long= as > all bindings are non-@code{nil}. > @end defmac > ``` > > Am I mistaken or is `while-let` a bit like a do..until loop that some > languages offer? Isn't it also like named-let? But without the ability to call itself recurs= ivey. I haven't tried it yet, but seems like while-let is a special case of named= -let, an "anonymous named-let" with conditions passed as-they-are. In other words= we could generate while-let as named-let with gensym as the name? (if cl-lib was all= owed in subr.el so to say). I am not sure if I have done it correctly, probably not= , but here is a try: (defmacro while-test (spec &rest body) (declare (indent defun)) (let* ((name (gensym "while-let-")) (bindings (if (and (consp spec) (symbolp (car spec))) (list spec) spec))) `(named-let ,name ,spec ,@body (if (not (and ,@(mapcar #'car bindings))) nil (,name ,@(mapcar #'cadr bindings)))))) ________________________________ Fr=E5n: Alfred M. Szmidt Skickat: den 10 november 2024 13:10 Till: Joost Kremers Kopia: eliz@gnu.org ; arthur.miller@live.com ; yuri.v.khan@gmail.com ; emacs-devel@gnu.or= g =C4mne: Re: Is this a bug in while-let or do I missunderstand it? @defmac while-let spec then-forms... Like @code{when-let*}, but repeat until a binding in @var{spec} is @code{nil}. The return value is always @code{nil}. The "Like FOO" is confusing -- it is not like when-let*, when-let* is also not like let*. E.g., when spec is (binding value) or just (value) (!?) -- which should be mentioned in the manual. These foo-LET are are mixing up the condition being tested and the binding, when there is no binding the form seems to be just a test as if you'd pass it directly to WHEN (or whatever). There should be some example that SPEC is not at all like in LET, and that: (when-let* ((result1 (do-computation)) ( (do-more result1))) (do-something result1)) is something like (I guess?): (let ((result1 (do-computation))) (when result1 (when (do-more result1) (do-something result2)))) And these mentions of "Like LET*" should be removed entierly. But this is a better, and a good start. @code{while-let} replaces a common pattern in which a binding is established outside the @{while}-loop, tested as part of the condition o= f @{while} and subsequently changed inside the loop using the same express= ion that it was originally bound to: @example (let ((result (do-computation))) (while result (do-stuff-with result) (setq result (do-computation)))) @end example Using @code{while-let}, this can be written more succinctly as: @example (while-let ((result (do-computation))) (do-stuff-with result)) @end example The binding of @code{result} is reestablished at every iteration, theref= ore setting the value of @code{result} inside the loop has no effect. In ord= er to end the loop, @code{(do-computation)} should eventually return @code{nil}. This example uses a single binding for clarity, but obviously @code{while-let} can establish multiple bindings. The loop runs as long = as all bindings are non-@code{nil}. @end defmac ``` Am I mistaken or is `while-let` a bit like a do..until loop that some languages offer? -- Joost Kremers Life has its moments --_000_DU2PR02MB10109373D5E48CFFBD2618000965F2DU2PR02MB10109eu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
>   @defmac while-let spec then-forms...
>   Like @code{when-let*}, but repeat until a binding in @var{spec}= is
>   @code{nil}.  The return value is always @code{nil}.
>
>The "Like FOO" is confusing -- it is not like when-let*, when= -let* is
>also not like let*.  E.g., when spec is (binding value) or just
>(value) (!?) -- which should be mentioned in the manual.
>
>These foo-LET are are mixing up the condition being tested and the
>binding, when there is no binding the form seems to be just a test as
>if you'd pass it directly to WHEN (or whatever).  There should be = some
>example that SPEC is not at all like in LET, and that:
>
>(when-let* ((result1 (do-computation))
>            (        = (do-more result1)))
>  (do-something result1))
>
>is something like (I guess?):
>
>(let ((result1 (do-computation)))
>  (when result1
>    (when (do-more result1)
>      (do-something result2))))
>
>And these mentions of "Like LET*" should be removed entierly.=
>
>But this is a better, and a good start.
>
>   @code{while-let} replaces a common pattern in which a binding i= s
>   established outside the @{while}-loop, tested as part of the co= ndition of
>   @{while} and subsequently changed inside the loop using the sam= e expression
>   that it was originally bound to:
>
>   @example
>   (let ((result (do-computation)))
>     (while result
>       (do-stuff-with result)
>       (setq result (do-computation))))
>   @end example
>
>   Using @code{while-let}, this can be written more succinctly as:=
>
>   @example
>   (while-let ((result (do-computation)))
>     (do-stuff-with result))
>   @end example
>
>   The binding of @code{result} is reestablished at every iteratio= n, therefore
>   setting the value of @code{result} inside the loop has no effec= t. In order
>   to end the loop, @code{(do-computation)} should eventually retu= rn
>   @code{nil}.
>
>   This example uses a single binding for clarity, but obviously
>   @code{while-let} can establish multiple bindings. The loop runs= as long as
>   all bindings are non-@code{nil}.
>   @end defmac
>   ```
>
>   Am I mistaken or is `while-let` a bit like a do..until loop tha= t some
>   languages offer?

Isn't it also like named-let? But without the ability to call itself recurs= ivey.
I haven't tried it yet, but seems like while-let is a special case of named= -let,
an "anonymous named-let" with conditions passed as-they-are. In o= ther words we could
generate while-let as named-let with gensym as the name? (if cl-lib was all= owed in
subr.el so to say). I am not sure if I have done it correctly, probably not= , but here
is a try:

(defmacro while-test (spec &rest body)
  (declare (indent defun))
  (let* ((name (gensym "while-let-"))
         (bindings (if (and (consp spec) (symbolp = (car spec)))
                     = ;  (list spec)
                     = ;spec)))
    `(named-let ,name ,spec
       ,@body
       (if (not (and ,@(mapcar #'car bindings)))
           nil
           (,name ,@(mapcar #'cadr bindings))= ))))
Fr=E5n: Alfred M. Szmidt &l= t;ams@gnu.org>
Skickat: den 10 november 2024 13:10
Till: Joost Kremers <joostkremers@fastmail.fm>
Kopia: eliz@gnu.org <eliz@gnu.org>; arthur.miller@live.com <= ;arthur.miller@live.com>; yuri.v.khan@gmail.com <yuri.v.khan@gmail.co= m>; emacs-devel@gnu.org <emacs-devel@gnu.org>
=C4mne: Re: Is this a bug in while-let or do I missunderstand it?
 
   @defmac while-let spec then-forms...<= br>    Like @code{when-let*}, but repeat until a binding in @var{spec= } is
   @code{nil}.  The return value is always @code{nil}.

The "Like FOO" is confusing -- it is not like when-let*, when-let= * is
also not like let*.  E.g., when spec is (binding value) or just
(value) (!?) -- which should be mentioned in the manual.

These foo-LET are are mixing up the condition being tested and the
binding, when there is no binding the form seems to be just a test as
if you'd pass it directly to WHEN (or whatever).  There should be some=
example that SPEC is not at all like in LET, and that:

(when-let* ((result1 (do-computation))
            ( &= nbsp;      (do-more result1)))
  (do-something result1))

is something like (I guess?):

(let ((result1 (do-computation)))
  (when result1
    (when (do-more result1)
      (do-something result2))))

And these mentions of "Like LET*" should be removed entierly.

But this is a better, and a good start.

   @code{while-let} replaces a common pattern in which a binding = is
   established outside the @{while}-loop, tested as part of the c= ondition of
   @{while} and subsequently changed inside the loop using the sa= me expression
   that it was originally bound to:

   @example
   (let ((result (do-computation)))
     (while result
       (do-stuff-with result)
       (setq result (do-computation))))
   @end example

   Using @code{while-let}, this can be written more succinctly as= :

   @example
   (while-let ((result (do-computation)))
     (do-stuff-with result))
   @end example

   The binding of @code{result} is reestablished at every iterati= on, therefore
   setting the value of @code{result} inside the loop has no effe= ct. In order
   to end the loop, @code{(do-computation)} should eventually ret= urn
   @code{nil}.

   This example uses a single binding for clarity, but obviously<= br>    @code{while-let} can establish multiple bindings. The loop run= s as long as
   all bindings are non-@code{nil}.
   @end defmac
   ```

   Am I mistaken or is `while-let` a bit like a do..until loop th= at some
   languages offer?


   --
   Joost Kremers
   Life has its moments


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