Re: [Caml-list] What is the fastest? Pattern matching or if then else

[Christos KK Loverdos <loverdos@gmail.com>]

On Dec 7, 2012, at 4:45 AM, Jacques Garrigue <garrigue@math.nagoya-u.ac.jp> wrote:

> On 2012/12/07, at 11:33, Francois Berenger <berenger@riken.jp> wrote:
> 
>> Hello,
>> 
>> I always wondered what is the fastest (at least for integers):
>> 
>> match n with
>> 0 -> (* do something *)
>> | _ -> (* do something else *)
>> 
>> or
>> 
>> if n = 0 then
>> (* do something *)
>> else
>> (* do something else *)
>> 
>> Sometimes I have some code that would be more beautiful
>> if I was using only pattern matching rather than
>> pattern matching interspersed with if then else directives.
>> 
>> Is one significantly faster than the other?
>> 
>> Is it the same cost at runtime?
> 
> $ ocaml -dlambda
>        OCaml version 4.00.1
> 
> # fun n -> match n with 0 -> "this" | _ -> "that";;
> (function n/1016 (if (!= n/1016 0) "that" "this"))
> - : int -> string = <fun>
> # fun n -> if n then "this" else "that";;
> (function n/1017 (if n/1017 "this" "that"))
> - : bool -> string = <fun>
> 
> In most cases, the two are going to be exactly equivalent.
> Here there is a slight difference because of the handling of the constant 0.
> But I would expect that to be optimized out in the native code compiler.
> So the short answer is:

> do not let your sense of beauty be disturbed by that.

+1

> 
> 	Jacques
> 
> 
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--
Christos KK Loverdos
@loverdos
stepsinscala.com

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