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[Caml-list] format type
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Date: -- (:)
From: Alessandro Baretta <alex@b...>
Subject: Re: [Caml-list] format type


Ken Wakita wrote:
> Did you try "%t"?
> 
> Printf.printf "%t": (out_channel -> unit) -> unit = <fun>

Since Cezary mentions parsing, I suppose he meant Scanf, 
rather than Printf.

> You could simply ignore out_channel if you are not interested.
> 
> Ken Wakita
> 
> 
>>From: Cezary Kaliszyk <ck189400@zodiac.mimuw.edu.pl>
>>Date: Sun, 3 Nov 2002 08:08:58 +0100
>>To: caml-list@inria.fr
>>Subject: [Caml-list] format type
>>
>>I'm trying to write a function that takes a format and a function and
>>applies some (got from elsewere) arguments to the function.
>>
>><snip>
>>
>>The only known workaround for me for now is to pass "%t" and
>>make my function not (unit -> unit) but ('a -> unit).

As far as I can see from the docs, "%t" is only meaningful 
with the Printf module. I see no mention of it in Scanf. 
What exactly are you trying to do anyway?

Assuming you are talking about the Scanf module, I'd say you 
can't. Of course, if your function takes a unit input, it 
can very well be a perfectly polymorphic function (à la 
ignore) with type ('a -> unit). In which case you can force 
a call to such function while scanning the input buffer by 
passing it a range conversion with an empty range: 
"%[^\000-\255]". Your function would be called with an empty 
string as an actual parameter.

Or, better yet, you can use the "%N" conversion, which 
passes the number of characters consumed. Just discard this 
value.

>>Writing code with changed types just for the sake of the language is
>>very bad. And with "%t" 'a seems to be (unit -> unit).

It is also very bad to complain without doing any work 
yourself. You are probably the only one on this list wishing 
to call a function with no input while parsing a buffer. 
Nothing wrong with this, apart from stylistic 
considerations, but it implies two things: 1) I don't 
suppose Pierre ever even thought of such a conversion for 
Scanf, and 2) even if he did, I doubt he'd care to implement 
it. If you really think it is necessary, you might consider 
hacking it into the Scanf module and submitting the patch to 
the maintainers.

Alex

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