Hamilton Richards writes: | In my previous example, | | > t = [0..] | > b = 3 : t | > c = 5 : t | | lists b and c share t, but in | | > x = 3 : [0..] | > y = 5 : [0..] | | lists x and y share nothing. Extensionally, they have the same | values as b and c, but each has its own copy of [0..]. | Unless, that is, the compiler is clever enough to recognize the | subexpression [0..] which x and y have in common. I don't know | whether any Haskell compilers look for common subexpressions, but | it's certainly an option. | So the question of whether names are "*the* (only) way" to | obtain sharing isn't really a language question-- it's more of a | compiler question. Hi. It's a difficult question for a compiler, especially as sharing isn't always a good thing. let t = [0..] b = 3 : t c = 5 : t in b !! (c !! 1000000) -- likely to have a space leak let x = 3 : [0..] y = 5 : [0..] in x !! (y !! 1000000) -- compact, unless transformed to gain sharing (The space leak arises because a million cells of t are allocated, but the garbage collector can't free them because they're still reachable via b.) Because of examples like that, I prefer to stick with a simple name-based sharing scheme. Regards, Tom