[Caml-list] Reason why 'for' doesn't work across floats?

[Caml-list] Reason why 'for' doesn't work across floats?

[Richard Jones]

Is there a particular reason why I shouldn't be allowed to step over
floats?

# for r = 0. to 9. step 1. do printf "%f" r done;;
          --
This expression has type float but is here used with type int

Rich.

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Re: [Caml-list] Reason why 'for' doesn't work across floats?

[Michal Moskal]

On Thu, Jan 08, 2004 at 02:11:52PM +0000, Richard Jones wrote:
> Is there a particular reason why I shouldn't be allowed to step over
> floats?
> 
> # for r = 0. to 9. step 1. do printf "%f" r done;;
>           --
> This expression has type float but is here used with type int

let f a b = for x = a to b do () done

What type would f have (int -> int -> int or float -> float -> float)?
One would need "for.", which doesn't seem appealing.

-- 
: Michal Moskal :: http://www.kernel.pl/~malekith : GCS {C,UL}++++$ a? !tv
: When in doubt, use brute force. -- Ken Thompson : {E-,w}-- {b++,e}>+++ h

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Re: [Caml-list] Reason why 'for' doesn't work across floats?

[Jacques Carette]

Michal Moskal <malekith@pld-linux.org> wrote:
> On Thu, Jan 08, 2004 at 02:11:52PM +0000, Richard Jones wrote:
> > Is there a particular reason why I shouldn't be allowed to step over
> > floats?
> > 
> > # for r = 0. to 9. step 1. do printf "%f" r done;;
> >           --
> > This expression has type float but is here used with type int
> 
> let f a b = for x = a to b do () done
> 
> What type would f have (int -> int -> int or float -> float -> float)?
> One would need "for.", which doesn't seem appealing.

Another reason is that
for r = 0. to 9. step 0.001 do printf "%f" r done;;
will not necessary have the expected number of iterations, since 9. will not be 'hit' exactly (numerical round-off 
guarantees that).  For some loops, the number of times around would change depending on whether all the numbers 
involved have exact base 2 representations or not.  Very ugly.

After suffering through painful debugging sesions on programs in languages that allow the above type of loops, I am 
quite glad that Ocaml does not allow this, even if in this case it is because of typing rather than sound numerical 
analysis...

Jacques

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Re: [Caml-list] Reason why 'for' doesn't work across floats?

[Richard Jones]

On Thu, Jan 08, 2004 at 04:03:58PM +0100, Michal Moskal wrote:
> On Thu, Jan 08, 2004 at 02:11:52PM +0000, Richard Jones wrote:
> > Is there a particular reason why I shouldn't be allowed to step over
> > floats?
> > 
> > # for r = 0. to 9. step 1. do printf "%f" r done;;
> >           --
> > This expression has type float but is here used with type int
> 
> let f a b = for x = a to b do () done
> 
> What type would f have (int -> int -> int or float -> float -> float)?
> One would need "for.", which doesn't seem appealing.

Perhaps 'a -> 'a -> 'a ?

Is this much different from the generic-but-not-really < operator in
OCaml?

Rich.

-- 
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Re: [Caml-list] Reason why 'for' doesn't work across floats?

[Artem Prisyznuk]

On Thu, 8 Jan 2004 15:47:59 +0000, Richard Jones <rich@annexia.org> wrote:
>> One would need "for.", which doesn't seem appealing.
>
> Perhaps 'a -> 'a -> 'a ?
>
> Is this much different from the generic-but-not-really < operator in
> OCaml?


Operator '<' - defined on any types, it's really polymorph operator.
But operator 'for' not has sences on string type.

-- 
Artem Prysyznuk
tema@sit.kiev.ua

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Re: [Caml-list] Reason why 'for' doesn't work across floats?

[Florian Hars]

Richard Jones wrote:
> On Thu, Jan 08, 2004 at 04:03:58PM +0100, Michal Moskal wrote:
>>>let f a b = for x = a to b do () done
>>
>>What type would f have (int -> int -> int or float -> float -> float)?
  >
> Perhaps 'a -> 'a -> 'a ?

So how many iterations would

f (Some (fun x -> x < "foobar"), None) (None, Some [| 1.2, 1.4, 1.6|])

perform?

Yours, Florian.

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