Lambda the Ultimate

The Fate Of LAMBDA in PLT Scheme v300
or
Lambda the Ultimate Design Flaw

About 30 years ago, Scheme had FILTER and MAP courtesy of Lisp hackers who missed them from their past experience. To this collection, Scheme added a lexically-scoped, properly-functioning LAMBDA. But, despite of the PR value of anything with Guy Steele's name associated with it, we think these features should be cut from PLT Scheme v300.

We think dropping FILTER and MAP is pretty uncontroversial; (filter P S) is almost always written clearer as a DO loop (plus the LAMBDA is slower than the loop). Even more so for (map F S). In all cases, writing the equivalent imperative program is clearly beneficial.

Why drop LAMBDA? Most Scheme users are unfamiliar with Alonzo Church (indeed, they don't even know that he was related to Guy Steele), so the name is confusing; also, there is a widespread misunderstanding that LAMBDA can do things that a nested function can't -- we still recall Dan Friedman's Aha! after we showed him that there was no difference! (However, he appears to have since lapsed in his ways.) Even with a better name, we think having the two choices side-by-side just requires programmers to think about their program; not having the choice streamlines the thought process, and Scheme is designed from the ground up to, as much as possible, keep programmers from thinking at all.

So now FOLD. This is actually the one we've always hated most, because, apart from a few examples involving + or *, almost every time we see a FOLD call with a non-trivial function argument, we have to grab pen and paper and imagine the *result* of a function flowing back in as the *argument* to a function. Plus, there are *more* arguments coming in on the side! This is all absurdly complicated. Because almost all the examples of FOLD we found in practice could be written as a simple loop with an accumulator, this style should be preferred, perhaps with us providing a simple helper function to abstract away the boilerplate code. At any rate, FOLD must fold.

--The PLT Scheme Team

This from the PLT Scheme mailing list. Clearly Guido's visionary thinking is having repercussions outside the world of Python. I, for one, welcome this change that can only benefit the Scheme language.