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To: caml-list@inria.fr
Cc: John.Harrison@cl.cam.ac.uk
Subject: Re: Functional composition operator? 
In-reply-to: Your message of "Tue, 08 Dec 1998 18:02:21 +0100."
             <199812081702.SAA29130@pauillac.inria.fr> 
Date: Tue, 08 Dec 1998 21:52:54 +0000
From: John Harrison <John.Harrison@cl.cam.ac.uk>
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Pierre Weis writes:

| In fact we discourage the usage of functional composition as a general
| programming tool

A very bad idea, in my opinion.

|  -- it only save a few characters in programs
|      (Compare
|       let h = f o g 
|       with
|       let h x = f (g x);;)
|  -- it breaks the polymorphism
|     (if defined as
|      let h = f o g 
|      h is not generalized, since its definition is a function
|      application, whereas inline expansion of functional composition
|      let h x = f (g x)
|      being the definition of a function is properly generalized.)

These alternatives are not semantically equivalent. If f and g are
complicated expressions that can be further evaluated, it is often
highly undesirable to perform the evaluation every time h is called,
which is what "let h x = f(g x)" entails. 

John.