[Caml-list] Puzzled by Scanf.Scanning.in_channel

[Caml-list] Puzzled by Scanf.Scanning.in_channel

[Diego Olivier Fernandez Pons]

    Caml-List,

When I try to use Scanf.fscanf with an input channel created with
Scanf.Scanning.from_string the type checker complains

    let s = Scanf.Scanning.from_string "3" in Scanf.fscanf s "%i" (fun x -> x);;

    Characters 55-56:
    Error: This expression has type Scanf.Scanning.in_channel
       but an expression was expected of type in_channel

Which confuses me as from the manual I understood this should have worked.

    val from_string : string -> in_channel

    Scanning.from_string s returns a formatted input channel which
reads from the given string. Reading starts from the first character
in the string. The end-of-input condition is set when the end of the
string is reached.

Could anyone explain how is the proper way to generate a input channel
from a string ? Its for testing a program that will use stdin in
production.

        Diego Olivier

Re: [Caml-list] Puzzled by Scanf.Scanning.in_channel

[Gabriel Scherer]

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You should use bscanf:

# Scanf.fscanf;;
- : in_channel -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>
# Scanf.bscanf;;
- : Scanf.Scanning.in_channel -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>


On Mon, Jun 4, 2012 at 8:59 PM, Diego Olivier Fernandez Pons <
dofp.ocaml@gmail.com> wrote:

>    Caml-List,
>
> When I try to use Scanf.fscanf with an input channel created with
> Scanf.Scanning.from_string the type checker complains
>
>    let s = Scanf.Scanning.from_string "3" in Scanf.fscanf s "%i" (fun x ->
> x);;
>
>    Characters 55-56:
>    Error: This expression has type Scanf.Scanning.in_channel
>       but an expression was expected of type in_channel
>
> Which confuses me as from the manual I understood this should have worked.
>
>    val from_string : string -> in_channel
>
>    Scanning.from_string s returns a formatted input channel which
> reads from the given string. Reading starts from the first character
> in the string. The end-of-input condition is set when the end of the
> string is reached.
>
> Could anyone explain how is the proper way to generate a input channel
> from a string ? Its for testing a program that will use stdin in
> production.
>
>        Diego Olivier
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa-roc.inria.fr/wws/info/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>
>

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Re: [Caml-list] Puzzled by Scanf.Scanning.in_channel

[Diego Olivier Fernandez Pons]

    Gabriel,

> You should use bscanf:
>
> # Scanf.fscanf;;
> - : in_channel -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>
> # Scanf.bscanf;;
> - : Scanf.Scanning.in_channel -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>

Thanks. My I ask what is the difference between in_channel and
Scanf.Scanning.in_channel ?

        Diego Olivier

Re: [Caml-list] Puzzled by Scanf.Scanning.in_channel

[Goswin von Brederlow]

Diego Olivier Fernandez Pons <dofp.ocaml@gmail.com> writes:

>     Gabriel,
>
>> You should use bscanf:
>>
>> # Scanf.fscanf;;
>> - : in_channel -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>
>> # Scanf.bscanf;;
>> - : Scanf.Scanning.in_channel -> ('a, 'b, 'c, 'd) Scanf.scanner = <fun>
>
> Thanks. My I ask what is the difference between in_channel and
> Scanf.Scanning.in_channel ?
>
>         Diego Olivier

Well, one is an in_channel and one is a Scanf.Scanning.in_channel. :)

You can look at the type definition of both of them in the source to see
the specific differences and similarities.

MfG
        Goswin