Equality

Equality is a nuanced thing. If we ask the question, is the string "hello" the same as the string "hello"? What do we really mean by “the same”?

  1. are they the same location in memory?

    We can test any two values for exact equivalence with eq?.

  2. for some values (numbers and strings, say) they might be in different locations in memory but they have the same value: 1 is 1 and so long as the strings are the same length (and type!) and each Unicode code point is the same in each index of the strings then they are “the same”

    We can test any two values for value equivalence with eqv?.

  3. Finally, for compound values, we can test if they are semantically the same with equal?.

    The Scheme R5RS standards suggests “do they print the same?”

    This woolly definition reflects the tricky problem of accessing the elements of compound values in a consistent manner.

equality.idio
n1 := 1
n2 := 2
n3 := 1
printf "(eq? n1 1) is %s\n" (eq? n1 1)
printf "(eq? n1 n2) is %s\n"(eq? n1 n2)
printf "(eqv? n1 n3) is %s\n" (eqv? n1 n3)

s1 := "hello"
s2 := "hello"
printf "(eq? s1 \"hello\") is %s\n" (eq? s1 "hello")
printf "(eq? s1 s2) is %s\n"(eq? s1 s2)
printf "(eqv? s1 \"hello\") is %s\n" (eqv? s1 "hello")
printf "(eqv? s1 s2) is %s\n" (eqv? s1 s2)

$ idio equality
(eq? n1 1) is #t
(eq? n1 n2) is #f
(eqv? n1 n3) is #t
(eq? s1 "hello") is #f
(eq? s1 s2) is #f
(eqv? s1 "hello") is #t
(eqv? s1 s2) is #t

Last built at 2024-12-21T07:11:29Z+0000 from 77077af (dev) for Idio 0.3