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[Caml-list] two unrelated questions
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Date: 2001-04-29 (21:12)
From: John Max Skaller <skaller@o...>
Subject: Re: [Caml-list] two unrelated questions
Mark Seaborn wrote:

> Another way of doing it is to CPS-convert the fold function to get
> something like:
> let rec foldc kons knil l = match l with
>   | [] -> knil
>   | x::xs -> kons x knil (fun rest -> foldc kons rest xs)

> This is more powerful than fold, but also harder to understand,

	You're not kidding, on both counts :-)

	It's also 'ugly', because it only works for lists,
but this is only because you hard coded the destructor.
Passing it as an argument:

  let rec foldc remove kons knil l = match remove l with
	| (_,None) -> knil
	| (xs,Some x) -> kons x knil (fun rest -> foldc remove kons rest xs)

  let foldc_list = foldc (fun l -> match l with 
		| [] -> l,None
		| x::xs -> xs,Some x)

It's a pity there is no such destructor for a Hashtbl. 
[All C++ STL data structures have read iterators, which 
amount to destructors]

John (Max) Skaller, mailto:skaller@maxtal.com.au
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
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