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How to add () to function parameters
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Date: 2009-10-14 (10:40)
From: Till Crueger <Till.Crueger@g...>
Subject: How to add () to function parameters

I am looking for a way to add a unit parameter to a function that takes an  
arbitrary number of parameters. If the number of parameters is known this  
is fairly easy and I can just do:

let lift1 f a =
    fun () ->
       f a;;

let lift2 f a b =
    fun () ->
      f a b;;

(all these create one closure per lifting)

However it is a bit of a hassle to have to code each of these lifts... So  
what I am looking for is a way to extend this pattern to all numbers. So  
far I got to the point that I can do the following:

let lift_once f a =
    fun () ->
       f a;;

let lift_more f a =
    fun () ->
       f () a;;

So for a function f taking two parameters a and b I can do

lift_more (lift_once f a) b
(two closures created)

and for a function taking the parameters a, b and c I can do

lift_more (lift_more (lift_once f a) b) c
(three closures created)

to get the lifted functions.

However this solution gets quite ugly with all the parentheses. Also there  
are a lot of closures being produced and evaluated for any single lifting.  
I had a look at the Jane Street blog post about variable argument  
functions (http://ocaml.janestcapital.com/?q=node/22), which seems to do  
similar things. However I have never been really good with CPS, so I don't  
know if those techniques can be applied to this problem.

Is there any way to do this, which does not get this ugly. Also the  
resulting lifted function should not contain too many closures.

Thanks for your help,