* list-set! Wrong type argument in position 1 (expecting mutable pair)
@ 2020-08-26 20:12 mbcladwell
2020-08-26 20:42 ` John Cowan
2020-08-26 20:43 ` Linus Björnstam
0 siblings, 2 replies; 3+ messages in thread
From: mbcladwell @ 2020-08-26 20:12 UTC (permalink / raw)
To: guile-user
Hi,
One shortcoming I find working with Guile is the limited number of
examples of how to use code. Consider list-set!. The only reference in
the entire Guile manual is the definition in section 6.6.9.6 List
Modification. If I google I find
https://docs.racket-lang.org/reference/pairs.html which gives me the
example (list-set '(zero one two) 2 "two") ==> '(zero one "two") which
is what I deduced from the Guile manual. If I try something similar
in Guile:
scheme@(guile-user)> (list-set! '("zero" "one" "twooooo") 2 "two")
ice-9/boot-9.scm:1669:16: In procedure raise-exception:
In procedure set-car!: Wrong type argument in position 1 (expecting
mutable pair): ("twooooo")
Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]> ,bt
1 (list-set! ("zero" "one" "twooooo") 2 "two")
In ice-9/boot-9.scm:
1669:16 0 (raise-exception _ #:continuable? _)
Could someone provide me with an example of how to use list-set! ?
Alternatively what I really need is how to modify a specified element
in a list.
Thanks
Mortimer
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: list-set! Wrong type argument in position 1 (expecting mutable pair)
2020-08-26 20:12 list-set! Wrong type argument in position 1 (expecting mutable pair) mbcladwell
@ 2020-08-26 20:42 ` John Cowan
2020-08-26 20:43 ` Linus Björnstam
1 sibling, 0 replies; 3+ messages in thread
From: John Cowan @ 2020-08-26 20:42 UTC (permalink / raw)
To: mbcladwell; +Cc: guile-user
First of all, Racket's pairs are immutable, so it provides list-set
(non-destructive) rather than list-set!.
Second, it is an error to mutate a literal, since that amounts to
self-modifying code. Some Schemes don't enforce that, but Guile does. So
you need (list-set! (list "one" "twoooo" three") 2 "two"), which constructs
the list at run time using the list function.
On Wed, Aug 26, 2020 at 4:13 PM <mbcladwell@stihie.net> wrote:
>
> Hi,
> One shortcoming I find working with Guile is the limited number of
> examples of how to use code. Consider list-set!. The only reference in
> the entire Guile manual is the definition in section 6.6.9.6 List
> Modification. If I google I find
> https://docs.racket-lang.org/reference/pairs.html which gives me the
> example (list-set '(zero one two) 2 "two") ==> '(zero one "two") which
> is what I deduced from the Guile manual. If I try something similar
> in Guile:
>
> scheme@(guile-user)> (list-set! '("zero" "one" "twooooo") 2 "two")
> ice-9/boot-9.scm:1669:16: In procedure raise-exception:
> In procedure set-car!: Wrong type argument in position 1 (expecting
> mutable pair): ("twooooo")
>
> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,bt
> 1 (list-set! ("zero" "one" "twooooo") 2 "two")
> In ice-9/boot-9.scm:
> 1669:16 0 (raise-exception _ #:continuable? _)
>
> Could someone provide me with an example of how to use list-set! ?
> Alternatively what I really need is how to modify a specified element
> in a list.
> Thanks
> Mortimer
>
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: list-set! Wrong type argument in position 1 (expecting mutable pair)
2020-08-26 20:12 list-set! Wrong type argument in position 1 (expecting mutable pair) mbcladwell
2020-08-26 20:42 ` John Cowan
@ 2020-08-26 20:43 ` Linus Björnstam
1 sibling, 0 replies; 3+ messages in thread
From: Linus Björnstam @ 2020-08-26 20:43 UTC (permalink / raw)
To: mbcladwell, guile-user
Literals are immutable. (list-set! '(1 2 3) 1 0) -> error.
(list-set! (list 1 2 3) 1 0) -> works
--
Linus Björnstam
On Wed, 26 Aug 2020, at 22:12, mbcladwell@stihie.net wrote:
>
> Hi,
> One shortcoming I find working with Guile is the limited number of
> examples of how to use code. Consider list-set!. The only reference in
> the entire Guile manual is the definition in section 6.6.9.6 List
> Modification. If I google I find
> https://docs.racket-lang.org/reference/pairs.html which gives me the
> example (list-set '(zero one two) 2 "two") ==> '(zero one "two") which
> is what I deduced from the Guile manual. If I try something similar
> in Guile:
>
> scheme@(guile-user)> (list-set! '("zero" "one" "twooooo") 2 "two")
> ice-9/boot-9.scm:1669:16: In procedure raise-exception:
> In procedure set-car!: Wrong type argument in position 1 (expecting
> mutable pair): ("twooooo")
>
> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,bt
> 1 (list-set! ("zero" "one" "twooooo") 2 "two")
> In ice-9/boot-9.scm:
> 1669:16 0 (raise-exception _ #:continuable? _)
>
> Could someone provide me with an example of how to use list-set! ?
> Alternatively what I really need is how to modify a specified element
> in a list.
> Thanks
> Mortimer
>
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-08-26 20:12 list-set! Wrong type argument in position 1 (expecting mutable pair) mbcladwell
2020-08-26 20:42 ` John Cowan
2020-08-26 20:43 ` Linus Björnstam
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