pcase without code duplication

pcase without code duplication

[michael-franzese]

I am using pcase, but am wondering whether I can have pcase
for 0 and 2 do the same things without adding a separate pcase
(0 and duplicating the statements.

(pcase orthogr-region
  (0 ... )    ; same operations as pcase 2
  (1 ... )
  (2 ... )    ; operations
  (_ ... ) )

Re: pcase without code duplication

[Óscar Fuentes]

michael-franzese@gmx.com writes:

> I am using pcase, but am wondering whether I can have pcase
> for 0 and 2 do the same things without adding a separate pcase
> (0 and duplicating the statements.
>
> (pcase orthogr-region
>   (0 ... )    ; same operations as pcase 2
>   (1 ... )
>   (2 ... )    ; operations
>   (_ ... ) )

(let ((xx 2))
  (pcase xx
    (1 (message "one"))
    ((or 0 2) (message "zero or two"))
    (_ (message "something else"))))

Re: pcase without code duplication

[michael-franzese]

Can one also use nil as option in pcase.  What possibilities
exist for (_ ?

e.g.

(nil
((or 0 nil)
((or _ nil)  

Regards
Michael


> Sent: Friday, April 23, 2021 at 3:24 PM
> From: "Óscar Fuentes" <ofv@wanadoo.es>
> To: help-gnu-emacs@gnu.org
> Subject: Re: pcase without code duplication
>
> michael-franzese@gmx.com writes:
> 
> > I am using pcase, but am wondering whether I can have pcase
> > for 0 and 2 do the same things without adding a separate pcase
> > (0 and duplicating the statements.
> >
> > (pcase orthogr-region
> >   (0 ... )    ; same operations as pcase 2
> >   (1 ... )
> >   (2 ... )    ; operations
> >   (_ ... ) )
> 
> (let ((xx 2))
>   (pcase xx
>     (1 (message "one"))
>     ((or 0 2) (message "zero or two"))
>     (_ (message "something else"))))
> 
> 
>

Re: pcase without code duplication

[Stefan Monnier]

> Can one also use nil as option in pcase.  What possibilities
> exist for (_ ?
>
> e.g.
>
> (nil

If you want to match a symbol, you need to quote it:

    ('nil (do-something))

> ((or 0 nil)

    ((or 0 'nil) (do-something-else))

Of course, you can also quote the 0 if you want, tho it makes no difference.

> ((or _ nil)  

This is redundant, but yes you can do

    ((or _ 'nil) (do-yet-another-thing))


-- Stefan

RE: [External] : Re: pcase without code duplication

[Drew Adams]

> > I am using pcase, but am wondering whether I can have pcase
> > for 0 and 2 do the same things without adding a separate pcase
> > (0 and duplicating the statements.
> >
> > (pcase orthogr-region
> >   (0 ... )    ; same operations as pcase 2
> >   (1 ... )
> >   (2 ... )    ; operations
> >   (_ ... ) )
> 
> (let ((xx 2))
>   (pcase xx
>     (1 (message "one"))
>     ((or 0 2) (message "zero or two"))
>     (_ (message "something else"))))

And even ordinary cl-case (aka case) will do,
if that's all you're doing.

(cl-case xx
  (1     (message "one"))
  ((0 2) (message "zero or two"))
  (t     (message "something else")))