Haha, I hadn't thought of that! That ability to create self-referential data is the main factor. That isn't really possible in lisp without some sort of letrec

Haha, I hadn't thought of that! That ability to create self-referential data is the main factor. That isn't really possible in lisp without some sort of letrec function, which this lisp shouldn't support. You would also have to watch out for recursive function definitions. Usually, the function body will just contain the symbol that refers to the function, which conceptually is similar to a straight pointer to the function, and someone might try to optimize it that way. In fact, with more thought, I realized the lazy evaluation is actually orthogonal to forming cyclic data. The "allOnes = 1 : allOnes" line doesn't necessarily form a cycle (depending on the interpreter/compiler, I imagine ghc and any other sensible implementation will form a cycle). Naively, this will just create a thunk which will get repeatedly evaluated, generating a long list of ones. EDIT: Nevermind, you're right.