Does pcase need progn in if condition

Does pcase need progn in if condition

[pietru]

Does "pcase" need progn in an "if" condition

--------

 (if condition

         (pcase n

	    (0  (save-excursion (insert s)))

    	    ((or 1 2 3 4 5)
	        (delete-region (point) b)
	        (save-excursion (insert s)))

            (_  (delete-region (point) b))) ))

Re: Does pcase need progn in if condition

[Christopher Dimech]

I do not think it needs a progn as it consists of a single expression.

> Sent: Friday, May 21, 2021 at 9:25 PM
> From: pietru@caramail.com
> To: "Help Gnu Emacs" <help-gnu-emacs@gnu.org>
> Subject: Does pcase need progn in if condition
>
>
> Does "pcase" need progn in an "if" condition
>
> --------
>
>  (if condition
>
>          (pcase n
>
> 	    (0  (save-excursion (insert s)))
>
>     	    ((or 1 2 3 4 5)
> 	        (delete-region (point) b)
> 	        (save-excursion (insert s)))
>
>             (_  (delete-region (point) b))) ))
>
>

Re: Does pcase need progn in if condition

[Emanuel Berg via Users list for the GNU Emacs text editor]

pietru wrote:

> Does "pcase" need progn in an "if" condition
>
>  (if condition
>
>          (pcase n
>
> 	    (0  (save-excursion (insert s)))
>
>     	    ((or 1 2 3 4 5)
> 	        (delete-region (point) b)
> 	        (save-excursion (insert s)))
>
>             (_  (delete-region (point) b))) ))
>

`if' should her better be `when'!

How `pcase' behaves within a when tho? Maybe depends on things
even INSIDE the when?

-- 
underground experts united
https://dataswamp.org/~incal

Re: Does pcase need progn in if condition

[Emanuel Berg via Users list for the GNU Emacs text editor]

Christopher Dimech wrote:

> I do not think it needs a progn as it consists of
> a single expression.

(while some-thing do)

(unless not-some-thing do)

(if something
    do-this <- `progn' here if >1
  else-do-that-1
  else-do-furthermore-this-2
  ...
  alright-done-n)

sometimes one can put useful things there, e.g. `let', and
avoid using progn for this reason

Yeah, progn is imbecile, almost. only, for some reason, prog1
is cool, and prog2 is weird.

(if t 1 2 3 4) ; 1

-- 
underground experts united
https://dataswamp.org/~incal

Re: Does pcase need progn in if condition

[Jean Louis]

* Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org> [2021-05-22 07:40]:
> sometimes one can put useful things there, e.g. `let', and
> avoid using progn for this reason
> 
> Yeah, progn is imbecile, almost. only, for some reason, prog1
> is cool, and prog2 is weird.
> 
> (if t 1 2 3 4) ; 1

`progn` returns the the last value:

(progn
  '(do-something)
  '(do-more)
  emacs-build-number) ⇒ 1

and is better looking then `let` when empty:

(let ()
  (message "hello")
  '(do-more)
  emacs-build-number) ⇒ 1

`prog1' is very handy as it will not return the last value but the value from 1st form:

Example is when you wish to return a value and after that informa a user like here below:

(cond ((= a 1) (do-something))
      (t (prog1 nil (message "Query shall be longer..."))))

After returning `report' it will message user about it. Maybe you
wish to return the status of a function and continue informing
user?

(defun function ()
  "Return REPORT"
  (prog1
      report
    (message report))) 

And `prog2' is more than this, it will return the value from 2nd
form, not third or first.

(prog2 
    (do-this-but-not-keep-return-value)
    (do-this-and-keep-and-return-value)
  (do-more-something-but-return-value-is-from-above))

-- 
Jean

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Re: Does pcase need progn in if condition

[Emanuel Berg via Users list for the GNU Emacs text editor]

Jean Louis wrote:

> `progn` returns the the last value:

The nth value...

> [progn] is better looking then `let` when empty:
>
> (let ()
>   (message "hello")
>   '(do-more)
>   emacs-build-number) ⇒ 1

Your example :)

> `prog1' is very handy as it will not return the last value
> but the value from 1st form:

:)

> Example is when you wish to return a value and after that
> informa a user like here below:
>
> (cond ((= a 1) (do-something))
>       (t (prog1 nil (message "Query shall be longer..."))))

...

> After returning `report' it will message user about it.
> Maybe you wish to return the status of a function and
> continue informing user?
>
> (defun function ()
>   "Return REPORT"
>   (prog1
>       report
>     (message report))) 

But you can do that with `let' as well and besides ... message
already does that? :O

(message "Oh, baby!") ; "Oh, baby!"

?

> And `prog2' is more than this, it will return the value from
> 2nd form, not third or first.

Some Elisp for you:

  cl-prog
  cl-prog*
  cl-progv
  cl-tagbody

-- 
underground experts united
https://dataswamp.org/~incal

Re: Does pcase need progn in if condition

[Jean Louis]

* Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org> [2021-05-22 12:33]:
> Some Elisp for you:
> 
>   cl-prog
>   cl-prog*
>   cl-progv
>   cl-tagbody

Those are Common Lisp emulation functions. I consider those good for
people used to Common Lisp. I used to be used to it, not any
more. cl-macs.el is macro package. So I find it good when it is
necessary to port some Common Lisp to Emacs Lisp. When writing new
code they never necessary.


-- 
Jean

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https://www.fsf.org/campaigns

Sign an open letter in support of Richard M. Stallman
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Re: Does pcase need progn in if condition

[Emanuel Berg via Users list for the GNU Emacs text editor]

Jean Louis wrote:

>> Some Elisp for you:
>> 
>>   cl-prog
>>   cl-prog*
>>   cl-progv
>>   cl-tagbody
>
> Those are Common Lisp emulation functions. I consider those
> good for people used to Common Lisp. I used to be used to
> it, not any more. cl-macs.el is macro package. So I find it
> good when it is necessary to port some Common Lisp to Emacs
> Lisp. When writing new code they never necessary.

Easy for you to say who write Lisp like it is Pascal...

-- 
underground experts united
https://dataswamp.org/~incal