Re: port-position return value

[Mario Domenech Goulart]

Hi Vincent,

On Thu, 6 Jan 2022 10:12:37 +0100 Vincent Aguiléra 
<vincent.aguilera@advizia.fr> wrote:

> I'm a new (and so far happy ;-) Chicken Scheme user.

Welcome!

> I'm facing a problem with port-position. The doc states that
> port-position "returns the current position of PORT as two values: row
> and column number".
>
> So this function should return a pair of values (whatever column
> number means). But in the tests I've made so far only the row number
> seems to be returned (tested on the default input port, on file ports
> and on string ports).

Not really a pair, but actually two values (as produced by the `values'
procedure).  CHICKEN provides some binding forms to support multiple
values (e.g., define-values, let-values, receive etc).  In CHICKEN they
are in the chicken.base module [0].  See also SRFIs 8 [1] and 11 [2],
for more detailed information.

[0] http://wiki.call-cc.org/man/5/Module%20(chicken%20base)#other-binding-forms
[1] https://srfi.schemers.org/srfi-8/srfi-8.html
[2] https://srfi.schemers.org/srfi-11/srfi-11.html

> Below are a code snippet and the corresponding csi output.
>
> Hope this list is appropriate for this kind of message!

Definitely!

> Thanks in advance for your help
>
> Vince
>
> =============
> (with-input-from-string "ab\ncd\nef"
>       (lambda ()
>               (port-for-each
>                       (lambda (c)
>                               (print c ': (port-position)))
>                       read-char))) 
> ==============
> CHICKEN
> (c) 2008-2021, The CHICKEN Team
> (c) 2000-2007, Felix L. Winkelmann
> Version 5.3.0 (rev e31bbee5)
> linux-unix-gnu-x86-64 [ 64bit dload ptables ]
>
> Type ,? for help.
> ; loading test.scm ...
> ; loading /usr/local/lib/chicken/11/chicken.port.import.so ...
> a:1
> b:1
>
> :2
> c:2
> d:2
>
> :3
> e:3
> f:3

That happens because `print' is not aware of multiple values and only
prints the first one.

You can try the following on csi:

  #;1> (port-position)
  2
  0
  ; 2 values
  #;2> (print (values 1 2))
  1
  #;3> (print (let-values (((x y) (values 1 2))) (cons x y)))
  (1 . 2)

I hope this helps.

All the best.
Mario
-- 
http://parenteses.org/mario