I like the way Haskell does it; equality is provided via the "Eq" typeclass. The language supports auto-deriving "Eq" instances that do a straightforward struct

I like the way Haskell does it; equality is provided via the "Eq" typeclass. The language supports auto-deriving "Eq" instances that do a straightforward structural and sub-structural equality check (e.g. if I have data Foo a b = Foo a b Int, then (Foo a1 b1 i1) == (Foo a2 b2 i2) = (a1 == a2) && (b1 == b2) && (i1 == i2)), but you can define it yourself it for types that have more representations than semantic values, like sets or maps or finger trees.