[Caml-list] AtomMap: build a list of all the elements in a map

[Caml-list] AtomMap: build a list of all the elements in a map

[Tie Cheng]

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Hello all,

I have posted a question on Caml-beginners, but have not got response so
far... guess maybe you could here...

I have defined "type AT = A AtomMap.t". Do you know how to build a function
"f: AT -> (atom * A) list" which returns a list of all the elements in a
map?

I am trying to combine AtomMap.fold, AtomMap.Iter (in this manual
http://cristal.inria.fr/~fpottier/alphaCaml/alphaCaml.pdf) to do so...
But it seems that unlike List.folder_left, AtomMap.fold does not accept list
as argument: val fold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b, there
it is not convenient to build a list progressively here...

Thanks and regards

Tie

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RE: [Caml-list] AtomMap: build a list of all the elements in a map

[David Allsopp]

Tie Cheng wrote:
> I have posted a question on Caml-beginners, but have not got 
> response so far... guess maybe you could here... I have defined 
> "type AT = A AtomMap.t". Do you know how to build a function 
> "f: AT -> (atom * A) list" which returns a list of all the 
> elements in a map?
> I am trying to combine AtomMap.fold, AtomMap.Iter 
> (in this manual http://cristal.inria.fr/~fpottier/alphaCaml/alphaCaml.pdf)
> to do so... But it seems that unlike List.folder_left, AtomMap.fold
> does not accept list as argument: val fold : (key -> 'a -> 'b -> 'b)
> -> 'a t -> 'b -> 'b, there it is not convenient to build a list 
> progressively here...

I don't see how that function signature differs from what you expect so sorry if that's because I don't know anything about alphaCaml!

What's wrong with:

fold (fun key value acc -> (key, value)::acc)) atomMap []

The signature for [fold] is simply like the signature for List.fold_right rather than List.fold_left.


David

Re: [Caml-list] AtomMap: build a list of all the elements in a map

[Raphael Proust]

On Mon, Feb 21, 2011 at 1:40 PM, Tie Cheng <chengtie@gmail.com> wrote:
> Hello all,
>
> I have posted a question on Caml-beginners, but have not got response so
> far... guess maybe you could here...
>
> I have defined "type AT = A AtomMap.t". Do you know how to build a function
> "f: AT -> (atom * A) list" which returns a list of all the elements in a
> map?

It seems that OCaml 3.12 introduced the function [bindings] which has
the type and semantic you're looking for.

>
> I am trying to combine AtomMap.fold, AtomMap.Iter (in this
> manual http://cristal.inria.fr/~fpottier/alphaCaml/alphaCaml.pdf) to do
> so... But it seems that unlike List.folder_left, AtomMap.fold does not
> accept list as argument: val fold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b ->
> 'b, there it is not convenient to build a list progressively here...

You should be able to combine fold and iter without the list conversion step:
let fold_iter iterator folder map init =
  AtomMap.fold (fun k e accu -> iterator k e; folder k e accu) map init

(I haven't actually tried the code, but something similar should do the trick)

-- 
_______
Raphael