My guess, without really knowing, is this is some sort of optimization. But it could affect things I suppose if someone is intending to construct lists for the main purpose of creating different eq-differentiated identifiers (eg as keys for a hasheq)...
Zelphir Kaltstahl writes: > Sorry, I misclicked "send" when I wanted to further edit my e-mail ... > > My Guile version is: > > ~~~~ > (version) > $6 = "3.0.4" > ~~~~ > > On 20.09.20 14:16, Zelphir Kaltstahl wrote: >> >> Hello Guile users, >> >> I just noticed something weird about eq?. >> >> My Guile version is: >> >> >> I get the different results, depending on whether I define some >> bindings in a let or using define: >> >> (In Emacs Geiser:) >> >> ~~~~ >> (define x '(10 9)) >> (define y '(10 9)) >> (eq? x y) >> $2 = #f >> >> (let ([x '(10 9)] >> [y '(10 9)]) >> (eq? x y)) >> $3 = #t >> ~~~~ >> >> Is this intentional or a bug? >> >> I first noticed something strange when writing the following code: >> >> ~~~~DEFINITION~~~~ >> (define make-multiple-list-remover >> (λ (equal-proc) >> (λ (lst unwanted) >> (let loop ([remaining-list lst]) >> (cond >> [(null? remaining-list) >> '()] >> [(equal-proc (car remaining-list) unwanted) >> (loop (cdr remaining-list))] >> [else >> (cons (car remaining-list) >> (loop (cdr remaining-list)))]))))) >> ~~~~ >> >> ~~~~TEST~~~~ >> (let ([a '(9 10)] >> [b '(9 10)]) >> (test-equal "make-multiple-list-remover-03" >> `(1 2 (3) (4) ,a) >> ((make-multiple-list-remover eq?) >> `(a b (c) (d) ,a) b))) >> ~~~~ >> >> I was wondering, why the test fails. I think (eq? ...) should not be >> able to see the equivalence of both lists a and b, just like when >> defined using (define ...). >> >> I can also run it in the REPL and see the difference: >> >> ~~~~ >> (define a '(9 10)) >> (define b '(9 10)) >> ((make-multiple-list-remover eq?) >> `(a b (c) (d) ,a) b) >> $4 = (a b (c) (d) (9 10)) >> >> (let ([a '(9 10)] >> [b '(9 10)]) >> ((make-multiple-list-remover eq?) >> `(a b (c) (d) ,a) b)) >> $5 = (a b (c) (d)) >> ~~~~ >> >> Somehow the bindings of let seem to be different from the bindings >> created using define. What about using define inside let? >> >> ~~~~ >> >> ~~~~ >> -- >> repositories: https://notabug.org/ZelphirKaltstahl > > Somehow the bindings of let seem to be different from the bindings > created using define. What about using define inside let? > > ~~~~ > (let ([unrelated 'bla]) > (define a '(9 10)) > (define b '(9 10)) > ((make-multiple-list-remover eq?) > `(a b (c) (d) ,a) b)) > $7 = (a b (c) (d)) > ~~~~ > > So there the define usage also differs from when I use define on the top > level. Perhaps that is the difference? On which level the bindings are > defined? > > Regards, > Zelphir
