From: Don Syme <dsyme@microsoft.com>
To: "'Pierre Weis'" <Pierre.Weis@inria.fr>, whitley@cse.buffalo.edu
Cc: caml-list@inria.fr
Subject: RE: Functional composition operator?
Date: Tue, 8 Dec 1998 12:09:49 -0800 [thread overview]
Message-ID: <39ADCF833E74D111A2D700805F1951EF0B2EF6A8@RED-MSG-06> (raw)
>
> -- it only save a few characters in programs
> (Compare
> let h = f o g
> with
> let h x = f (g x);;)
As you say, you can always define the infix identifier, so there's no
hassle, i.e. I'm not complaining. However, the comparison should be
f1 << f2 << f3 << f4
v.
(fun x -> f1(f2(f3(f4 x))))
because we may not be binding the on-the-fly value to a name. Saving
parentheses is clearly a good idea - most the ML syntax is directed to this.
Even worse consider
f1 << f2 x y z << f3 << f4 a b
v.
(let f4' = f4 a b in
let f2' = f2 x y z in
(fun x -> f1(f2' z(f3(f4' x)))))
since in the latter case we may be taking advantage of the partial
evaluation of the closures to, for example, precompute some tables based on
the information in x,y,z and a,b. I know which I prefer!
In 16,000 lines implementing the interactive theorem prover DECLARE there
are 220 uses of composition, so one every 70 lines or so. There are 500
uses of "map", so it's relatively common in that one random example at
least.
Cheers,
Don
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------------------------------------------------------------------------
next reply other threads:[~1998-12-09 9:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
1998-12-08 20:09 Don Syme [this message]
-- strict thread matches above, loose matches on Subject: below --
1998-12-09 12:00 Don Syme
1998-12-08 19:51 Don Syme
1998-12-08 18:08 Andrew Kay
1998-12-08 20:32 ` John Prevost
1998-12-09 16:17 ` Anton Moscal
1998-12-08 5:23 John Whitley
1998-12-08 17:02 ` Pierre Weis
1998-12-08 21:52 ` John Harrison
1998-12-09 10:58 ` Pierre Weis
1998-12-09 17:17 ` John Harrison
1998-12-11 13:57 ` Pierre Weis
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