Re: procedure to check equality of list-elements

[Jean Abou Samra]

Le 06/11/2022 à 13:03, Thomas Morley a écrit :
> Hi,
>
> in !1701 `ly:beam::calc-knee' checks whether all list-elements are equal.
> Basically doing (apply eqv? <number-list>).
> Tbh, I don't understand why it works...


eqv? has no problem working on more than two elements.

scheme@(guile-user)> (eqv? 1 1)
$1 = #t
scheme@(guile-user)> (eqv? 1 2)
$2 = #f
scheme@(guile-user)> (eqv? 1 1 1)
$3 = #t
scheme@(guile-user)> (eqv? 1 1 2)
$4 = #f
scheme@(guile-user)> (eqv? 1 1 1 1)
$5 = #t
scheme@(guile-user)> (eqv? 1 2 3 4)
$6 = #f
scheme@(guile-user)> (eqv?)
$7 = #t



This is similar to how in other languages you have to
repeat the + operator (a+b+c+d) whereas in Scheme you
can do (+ a b c d).



> Though, the need to check a list for all list-elements are equal
> happened to me not only once.
> Thus, would it be acceptable to add something like:
>
> (define* (equal-list-elts? list #:optional (proc eq?))
>    (apply proc list))
>
> to lily-library.scm?



What would be the point? Do you dislike (apply proc lst)?

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