[Caml-list] let rec with let ref

[Caml-list] let rec with let ref

[Antoine Rimlet]

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Hi,

I'm trying to write a recursive function that would work like a for loop:

let rec forloop g v u =
  let x = ref v in let rec h = begin g !x; x := !x + 1; if !x <= u then h
end
  in h;;

I know this is horribly far from the functional spirit, but anyway ocaml
complains that "This kind of expression is not allowed as right-hand side
of `let rec'". It seems to me that this function definition has a meaning,
so why is it rejected? What should I do to get it accepted by ocaml?

Many thanks in advance,

Antoine

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Re: [Caml-list] let rec with let ref

[vrotaru.md]

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let rec h () = ... then h ()...

will define (and apply a function)

Iet rec value = .. value

is something totally different

În joi, 17 mar. 2016 la 17:33, Antoine Rimlet <antoine.rimlet@gmail.com> a
scris:

> Hi,
>
> I'm trying to write a recursive function that would work like a for loop:
>
> let rec forloop g v u =
>   let x = ref v in let rec h = begin g !x; x := !x + 1; if !x <= u then h
> end
>   in h;;
>
> I know this is horribly far from the functional spirit, but anyway ocaml
> complains that "This kind of expression is not allowed as right-hand side
> of `let rec'". It seems to me that this function definition has a meaning,
> so why is it rejected? What should I do to get it accepted by ocaml?
>
> Many thanks in advance,
>
> Antoine
>
>

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Re: [Caml-list] let rec with let ref

[Goswin von Brederlow]

On Thu, Mar 17, 2016 at 03:37:32PM +0000, vrotaru.md@gmail.com wrote:
> let rec h () = ... then h ()...
> 
> will define (and apply a function)
> 
> Iet rec value = .. value
> 
> is something totally different
> 
> În joi, 17 mar. 2016 la 17:33, Antoine Rimlet <antoine.rimlet@gmail.com> a
> scris:
> 
> > Hi,
> >
> > I'm trying to write a recursive function that would work like a for loop:
> >
> > let rec forloop g v u =
> >   let x = ref v in let rec h = begin g !x; x := !x + 1; if !x <= u then h
> > end
> >   in h;;
> >
> > I know this is horribly far from the functional spirit, but anyway ocaml
> > complains that "This kind of expression is not allowed as right-hand side
> > of `let rec'". It seems to me that this function definition has a meaning,
> > so why is it rejected? What should I do to get it accepted by ocaml?
> >
> > Many thanks in advance,
> >
> > Antoine

Also why use a ref? You need to define a function, not a value here anyway.

let rec h x = ... then h (x+1)
in h v

MfG
	Goswin

Re: [Caml-list] let rec with let ref

[Christoph Höger]

You should use this variant:

let forloop g v u =
  let x = ref v in let rec h () = begin g !x; x := !x + 1; if !x <= u
then h ()
end
  in h;;

1. forloop does not need to be recursive (and is not a syntactical function)
2. h is not a syntactical function, but can easily be made one.
Recursive functions need to be syntactical functions (i.e.
lambda-abstractions) in order to correctly compile them.

regards,

Christoph

Am 18.03.2016 um 12:36 schrieb Goswin von Brederlow:
> let rec forloop g v u =
>> >   let x = ref v in let rec h = begin g !x; x := !x + 1; if !x <= u then h
>> > end
>> >   in h;;


-- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin

Tel.: +49 (30) 314-24890
E-Mail: christoph.hoeger@tu-berlin.de