Comments on: Toolchest: Shortcuts for higher-order functions

By: Michael T

Michael T — Tue, 08 Jan 2008 01:43:31 +0000

Lambda can indeed be used to represent recursive functions. That is the point of the Y combinator, after all. Although your point is still well taken for every day programming. The recursive representation of factorial using only lambdas - no side effects in the environment - is not the first way most people would think to do it. So when you say ‘cannot be used to represent recursive functions’, I agree if you mean ‘no sane person would use it to represent recursive in code other people would read’. But in an absolute sense, you CAN represent recursive functions using lambdas.

By: Szymon

Szymon — Tue, 18 Dec 2007 08:55:18 +0000

Why not:

(mapcar (* 2 _) ‘(1 2 3))

By: Mork

Mork — Tue, 18 Dec 2007 05:11:43 +0000

I don’t understand why anybody would choose ‘for’ if aiming for conciseness: It is neither particularly short nor descriptive (if three-letter names are necessary (it eludes me why that might be), ‘fun’ strikes me as a better compromise).

Why not use the Greek lambda character (λ) itself? Any useful editor or operating system should provide shortcuts to insert that character with at most two keystrokes.
But since I’ve never found it a problem to type out ‘lambda’, I prefer Emacs’ pretty-lambda mode: You type (lambda (x) …) and it displays as (λ (x) …) — the actual source code is not modified, only the way ‘lambda’ is displayed on screen. This works with all existing code, it doesn’t require any custom set-up other than a line or two in your .emacs, and it doesn’t confuse anybody else reading your code.

By: admin

admin — Tue, 18 Dec 2007 05:04:53 +0000

@_deepfire: Any suggestions for a choice of letters?

By: admin

admin — Tue, 18 Dec 2007 04:18:01 +0000

Here is a description and explanation of the CUT macro:

http://srfi.schemers.org/srfi-26/srfi-26.html

By: _deepfire

_deepfire — Tue, 18 Dec 2007 00:23:49 +0000

Ok, I messed up the letters in the previous comment, but the problem should be obvious by now — that specific choice of letters isn’t providing a terribly clear idea about what’s happening.

By: _deepfire

_deepfire — Tue, 18 Dec 2007 00:21:08 +0000

#L being CURRY asks for a RCURRY companion, but #R is already taken..

By: Matthew Swank

Matthew Swank — Mon, 17 Dec 2007 23:28:42 +0000

Here’s is another implementation of cut/cute based closely on the srfi-26 reference implementation: http://paste.lisp.org/display/52700

By: admin

admin — Mon, 17 Dec 2007 18:54:46 +0000

@Mark: There’s some extra code required. I linked to it in the introduction, but here it is again:

http://paste.lisp.org/display/52651

By: Anonymous

Anonymous — Mon, 17 Dec 2007 18:33:54 +0000

I’d just use (mapcar (lambda (x) (* x 2)) list). If that’s too “long-winded”, I suggest you give pretty-lambdas.el a try.