I should have included a link in my answer to Richard O'Keefe.

Here is the Squeak Swiki Page I was talking about: http://minnow.cc.gatech.edu/squeak/331 It's called "Are Squeak blocks like Scheme blocks"

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"'do' is also defined in terms of rewriting to a recursive 'lambda'."

Anyway I don't really understand how recursive lambdas can give you iteration while reusing the same environment - recursion creates a new environment with each call. Yes I know about tail recursion - but if you were to capture a variable in a Scheme recursive loop (that is store a closure accessing that variable), as the Swiki example does with a Smalltalk iteration loop, then each iteration WOULD have to be a separate variable. I think that if a variable is captured then the tail recursion optimization must be disallowed.

Think about what recursion looks like in C. void RecureLoop(int i) { if (i<10) RecureLoop(i+1); ...

If you call RecureLoop(1), then when i=10 that means there is another instance of i on the stack that holds a 9, another above that with an 8 another above that with a 7... You can see that capturing a variable in a recursive lambda iteration means that each captured variable is unique.

Thus "Scheme _does_ create a new environment (in principle) for each loop _entry_ but not for each loop _iteration_." is only true when the tail recursion optimization succeeds and that can only happen if the environment isn't captured.

Anyway, in Smalltalk iteration is primary, not recursion. Is there a tail-recusion optimization?

But now that I think about it, the only loops that are primitive right now are while and number to: loops... Won't blocks have to create a new environment on each invocation? And primitive looping blocks are the only blocks that will know the difference between running the first first time and running again, so therefor any block sent to collect: will be nested inside of a primitive iterator, but being nested in the iteration block not being the iteration block the they won't know the difference between a first invocation and a second one and so they'll have to create a new environment each time.

Am I missing something?

Joshua Scholar