* Passing function to mapcar
@ 2024-09-01 23:44 Heime
2024-09-02 9:04 ` Stephen Berman
2024-09-02 9:35 ` Joost Kremers
0 siblings, 2 replies; 3+ messages in thread
From: Heime @ 2024-09-01 23:44 UTC (permalink / raw)
To: Heime via Users list for the GNU Emacs text editor
I am using mapcar to apply the lambda function taking values
in rgb-list as argument c.
(mapcar (lambda (c)
(min 255 (max 0 (round (* c factor)))))
rgb-list)
I think that the function used for mapcar should have only a
single argument. Is this correct ?
What can one do if I want to call a function with more than
a single argument ?
(defun myfunc (c factor)
(min 255 (max 0 (round (* c factor)))))
(mapcar myfunc(c factor) rgb-list)
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Passing function to mapcar
2024-09-01 23:44 Passing function to mapcar Heime
@ 2024-09-02 9:04 ` Stephen Berman
2024-09-02 9:35 ` Joost Kremers
1 sibling, 0 replies; 3+ messages in thread
From: Stephen Berman @ 2024-09-02 9:04 UTC (permalink / raw)
To: Heime; +Cc: Heime via Users list for the GNU Emacs text editor
On Sun, 01 Sep 2024 23:44:03 +0000 Heime <heimeborgia@protonmail.com> wrote:
> I am using mapcar to apply the lambda function taking values
> in rgb-list as argument c.
>
> (mapcar (lambda (c)
> (min 255 (max 0 (round (* c factor)))))
> rgb-list)
>
> I think that the function used for mapcar should have only a
> single argument. Is this correct ?
Yes.
> What can one do if I want to call a function with more than
> a single argument ?
>
> (defun myfunc (c factor)
> (min 255 (max 0 (round (* c factor)))))
>
> (mapcar myfunc(c factor) rgb-list)
If you redefine `myfunc' to make `factor' the first argument and `c' the
second, you can use apply-partially; maybe that does what you want:
(let ((rgb-list '(37 157 217))
(factor 0.7))
(mapcar (apply-partially #'myfunc factor) rgb-list))
=>
(26 110 152)
(If `factor' is always a single number you don't need to redefine
`myfunc', since multiplication is commutative, but then the argument `c'
is assigned the value of `factor' in the call to apply-partially and the
argument `factor' gets the respective values of `rgb-list', so
conceptually it's better to switch the arguments.)
Steve Berman
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Passing function to mapcar
2024-09-01 23:44 Passing function to mapcar Heime
2024-09-02 9:04 ` Stephen Berman
@ 2024-09-02 9:35 ` Joost Kremers
1 sibling, 0 replies; 3+ messages in thread
From: Joost Kremers @ 2024-09-02 9:35 UTC (permalink / raw)
To: Heime; +Cc: Heime via Users list for the GNU Emacs text editor
On Sun, Sep 01 2024, Heime wrote:
> I am using mapcar to apply the lambda function taking values
> in rgb-list as argument c.
>
> (mapcar (lambda (c)
> (min 255 (max 0 (round (* c factor)))))
> rgb-list)
>
> I think that the function used for mapcar should have only a
> single argument. Is this correct ?
Yup.
> What can one do if I want to call a function with more than
> a single argument ?
There's seq-mapn.
--
Joost Kremers
Life has its moments
^ permalink raw reply [flat|nested] 3+ messages in thread
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