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Comment by busterarm | Hacker News Reader

How does one Lisp without TCO?

(Yes, I know some do without, but usually not without a great reason...for example Clojure needing to maintain JVM calling conventions)

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Scheme guarantees TCO, but not Lisp in general I think. I seem to remember that Common Lisp does not guarantee TCO either.

Common Lisp does not guarantee it, but a few implementations do provide it

https://0branch.com/notes/tco-cl.html

One focuses on the learning aspects rather than creating a production lisp. If you want a production lisp, there are plenty out there.

And regardless, adding TCO is relatively simple as well, so not exactly a hard problem to figure out after you've written the first version of your toy lisp.

We're talking about Lisp in Python here. Python itself famously[1,2] refuses to have TCO.

1: http://neopythonic.blogspot.com/2009/04/tail-recursion-elimi... 2: http://neopythonic.blogspot.com/2009/04/final-words-on-tail-...

Here is a lisp implementation (mal) with TCO, written in Python:

- https://github.com/kanaka/mal/blob/master/impls/python/step5...

- Theory: https://github.com/kanaka/mal/blob/master/process/guide.md#s...

You can implement TCO in Python manually with continuation-passing style and trampolines.

Common Lisp doesn't guarantee TCO, and yet people manage just fine

Generally, by doing actual work instead of linear recursion exercises.

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