Re: procedure to check equality of list-elements

[Jean Abou Samra]

Le 06/11/2022 à 16:13, Luca Fascione a écrit :
> Note the detail that + a b c and eq? a b c don't do the exact same thing:
>
> + a b c is equivalent to (a + b) + c
> eq? a b c is equivalent to (a == b) && (b == c)


Yes. On the other hand, Scheme (+ a b c d) behaves like Python a+b+c+d, 
and Scheme (equal? a b c d) behaves (I mean, not on details like how 
things are actually compared, but logically) like Python a == b == c == 
d (whereas in C/C++ the expression a == b == c == d  is evaluated as 
(((a == b) == c) == d).


> The list form has short circuiting if I remember right (eq? bails out 
> on the first false it finds), but I don't remember how evaluation 
> works for the arguments, in terms of what side effects are meant to 
> observable when early-out happens

eq?, eqv? and equal? are procedures (= functions). Therefore, Scheme not 
being a lazy language, all inner arguments are first evaluated and any 
side effects are observable. On the other hand, "and" and "or" are 
macros, with lazy behavior.

Best,
Jean

OpenPGP_signature
Description: OpenPGP digital signature