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Date: Fri, 11 Jan 2002 10:23:34 +0100
From: Xavier Leroy <xavier.leroy@inria.fr>
To: John Prevost <jprevost@libcom.com>
Cc: caml-list@inria.fr, romildo@uber.com.br
Subject: Re: [Caml-list] Function definition with multiple patterns in multiple equations
Message-ID: <20020111102334.A7963@pauillac.inria.fr>
References: <20020108110836.A9147@darling.home.br> <20020108082639.A87628@libcom.com>
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> Anyway, the quick-n-dirty method of doing multiple patterns like
> your example is to write:
> 
> let f a b = match (a,b) with
>   | (0, 0) -> 1
>   | (_, _) -> 0  
> 
> But, this may very well have the overhead of actually building a
> pair.

Not in Objective Caml.  There's a special optimization in both the
bytecode and native-code compilers to avoid the construction of the
pair in this case.

  You can also decompose it into something like:
> 
> let f = function
>   | 0 -> (function
>             | 0 -> 1
>             | _ -> 0)
>   | _ -> 0
> 
> Which is, yes, rather unattractive for such a small example.

That should be:
 let f = function
   | 0 -> (function
             | 0 -> 1
             | _ -> 0)
   | _ -> (function _ -> 0)

And it would be less efficient due to the extra function invocation
involved.  (Assuming f is generally applied to two arguments; if you
do a lot of partial applications of f, the latter might be slightly
more efficient.)

- Xavier Leroy
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