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[Caml-list] Q: Correct locations for macro camlp4 extensions
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Date: 2004-08-24 (07:43)
From: Marcin 'Qrczak' Kowalczyk <qrczak@k...>
Subject: Re: [Caml-list] Q: Correct locations for macro camlp4 extensions
W li¶cie z pon, 23-08-2004, godz. 19:16 -0400, Michael Alexander Hamburg

> Another syntax construction that I might write up (which I'm not aware of
> in any programming language) would be something like
> (f _ x _ _ y) translates into (fun p1 p2 p3 -> f p1 x p2 p3 y)

My language Kogut uses this (along with _ in patterns as in other
functional languages). Note: these expressions are evaluated once,
not each time the function is applied.

> When I have n lists of pairs to sort by the
> first element of the tuple, or some other function like that, it saves me
> a significant amount of programming effort to write
> # let (<-<<) f g a b = f (g a) (g b);;
> or
> # let sort_by g a b = sort (compare (g a) (g b));;

It may be better to perform Schwartzian transform: make a list of
(g x, x) pairs, sort it, and extract elements back. It applies g
O(N) rather than O(N log N) times.

Well, unless g is as simple as fst.

   __("<         Marcin Kowalczyk
   \__/       qrczak@knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/

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