Variables are uniquely named at parse time, but after one beta step, you have two distinct instances each of x and y, albeit in different scopes, and after a second beta step, you have two distinct variables named y in the same scope.
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This doesn't come up in most mainstream languages, but Zig and Jai are getting people excited about comptime evaluation, and dependent types need comptime evaluation as well. Uniqueness is fine until you're doing higher-order evaluation in your compilation pipeline like this, which will be more and more desirable in the future, at least if the current trends are any indication.
The semantics are the same for the user and debugging works, which is what matters.
If you're using an object oriented language for implementation then this is already the computational cost. If you're using a functional language then yes there is some space overhead because it breaks sharing but that's the price. Was there something else you were thinking of?
It's not just space overhead, it requires you to recursively walk the argument of the application and replace all variables with fresh ones, once for every occurrence of the function argument. This means that function application is no longer O(size of the function) but rather O(size of the function + occurrences of the argument * size of the argument). If the size of the argument is big this makes the function application much much slower.
" What happens in the evaluator when you have
(\ a . a a) (\ x . \ y . x y)
Variables are uniquely named at parse time, but after one beta step, you have two distinct instances each of x and y, albeit in different scopes, and after a second beta step, you have two distinct variables named y in the same scope. "
This doesn't come up in most mainstream languages, but Zig and Jai are getting people excited about comptime evaluation, and dependent types need comptime evaluation as well. Uniqueness is fine until you're doing higher-order evaluation in your compilation pipeline like this, which will be more and more desirable in the future, at least if the current trends are any indication.