Re: [Caml-list] format strings

[Jiten Pathy <jpathy@fssrv.net>]

nvm. make_printf is what I am after. Some complicated stuff is going
on in CamlInternalFormat.

On Mon, Feb 9, 2015 at 5:05 PM, Jiten Pathy <jpathy@fssrv.net> wrote:
> Is there a way I can define a function which has the same signature of
> printf family but is a no-op?
>
> f : ('a, 'b, unit) format -> 'a
>
> assert(f "%s %d" "hello" 1 = ());;
>
> On Mon, Feb 9, 2015 at 9:32 AM, David Allsopp <dra-news@metastack.com> wrote:
>> Jiten Pathy wrote:
>>> When i define a wrapper around format functions like
>>>
>>> let f s = (fun x -> Printf.sprintf s x);;
>>>
>>> val f : ('a -> 'b, unit, bytes) format -> 'a -> 'b = <fun>
>>>
>>> I am confused about the inferred type. where does this 'b comes from?
>>
>> Your wrapper carries the requirement that the format [s] must have at least one %-parameter. Writing without the fun might make this more obvious:
>>
>> let f s x = Printf.sprintf s x
>>
>> The 'a -> 'b is the encoding of this requirement. f "foo" will type. If instead you wrote:
>>
>> let f s = Printf.sprintf s
>>
>> you'd get the type you're expecting: ('a, unit, bytes) format -> 'a
>>
>> and you can have format strings with no %-parameters (so f "foo" now types). If you meant to have it so that the format string must have *exactly* one %-parameter then you need an annotation:
>>
>> let f s x : string = Printf.sprintf s x
>>
>> and now f "%d" will type, but f "%s %d" will not.
>>
>> HTH,
>>
>>
>> David