Re: [Caml-list] Strange online ocamldoc for Scanf

[Dominique Martinet <asmadeus77@gmail.com>]

Francois BERENGER wrote on Tue, Sep 04, 2018:
> > ('a, 'b, 'c, 'd) scanner is itself a function taking two arguments, as
> > defined a bit later in the page:
> > 
> > type ('a, 'b, 'c, 'd) scanner = ('a, Scanning.in_channel, 'b, 'c, 'a -> 'd, 'd) format6 ->
> >        'c
> 
> Ok, my mistake.
> 
> I have to admit that I don't understand such a (lengthy) type
> definition, probably because I don't read such ones very often.

Well, to be fair, it doesn't say "two arguments" here -- 'c happens to
be a function itself...

What's important is there is an arrow (->) in the type definition so a
scanner is a function, and which can return any type 'c when given a
format, so depending on what you give it you'll get something else.


I think it's interesting to play with it in the toplevel:

# open Scanf;;
# Scanf.sscanf;;
- : string -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>
# let s = Scanf.sscanf "15" "%d";;  
val s : (int -> '_weak1) -> '_weak1 = <fun>
# s (fun d -> "something");;
- : string = "something"
# s;;
- : (int -> string) -> string = <fun>


So when I first assigned 's' I got a function, which takes in argument a
function expecting and int and returning "something"
The '_weak1 here is like 'a except that it "solidifies" on first use,
as you can see after calling 's' with a function once it will expect
that all further use of 's' will be with a string-returning function


Good luck,
-- 
Dominique

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