Re: [Caml-list] ignore semantics

[Philippe Veber <philippe.veber@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1224 bytes --]

Hi John,

That's a good reason indeed, good enough to justify having this special
case semantics. Thanks!

ph.


2012/12/17 John Whitington <john@coherentgraphics.co.uk>

> Hi,
>
>
> Philippe Veber wrote:
>
>> This is a rather minor issue, but I was surprised by the following
>> answers of the interpreter:
>>
>>          OCaml version 4.00.1
>>
>> # ignore succ;;
>> Warning 5: this function application is partial,
>> maybe some arguments are missing.
>> - : unit = ()
>> # (fun _ -> ()) succ;;
>> - : unit = ()
>>
>> I naively used to think the two expressions were equivalent. Reading
>> pervasives.mli, I found that ignore is a primitive:
>>
>> external ignore : 'a -> unit = "%ignore"
>>
>> which means it is treated as a special case. Just for curiosity, what is
>> the rationale for the warning in the first case?
>>
>
> Imagine you wrote:
>
> ignore (output_something_and_return_**something)
>
> When what you wanted was
>
> ignore (ouput_something_and_return_**something ())
>
> You'd want the partial application error there, even though you are
> (intentionally) ignoring the return value of the function.
>
> Cheers,
>
> --
> John Whitington
> Director, Coherent Graphics Ltd
> http://www.coherentpdf.com/
>
>

[-- Attachment #2: Type: text/html, Size: 1907 bytes --]