Re: binary-port?

[Marco Maggi]

Ludovic Courtès wrote:

>>> However,  I’m  wondering  whether  we  should  not  just
>>> squarely do away with the binary/textual distinction

How would you handle port position?  From R6RS[1]:

  (port-has-port-position? port) procedure
  (port-position port) procedure

    The port-has-port-position? procedure  returns #t if the
    port  supports  the   port-position  operation,  and  #f
    otherwise.

    For a  binary port, the  port-position procedure returns
    the index of  the position at which the  next byte would
    be  read  from  or  written  to the  port  as  an  exact
    non-negative  integer   object.  For  a   textual  port,
    port-position     returns     a     value    of     some
    implementation-dependent  type  representing the  port’s
    position;  this value  may  be useful  only  as the  pos
    argument  to   set-port-position!,  if  the   latter  is
    supported on the port (see below).

    If   the   port   does   not  support   the   operation,
    port-position  raises an  exception with  condition type
    &assertion.

      Note: For a textual port, the port position may or may
      not be an integer object.  If it is an integer object,
      the integer object  does not necessarily correspond to
      a byte or character position.

  (port-has-set-port-position!? port) procedure
  (set-port-position! port pos) procedure

    If port is  a binary port, pos should  be a non-negative
    exact  integer object. If  port is  a textual  port, pos
    should be the return value of a call to port-position on
    port.

  I  do  not  know  how  current  Guile  handles  ports;  if
internally  you mark a  binary port  to handle  the position
char-wise (so  that it  is meant to  be a textual  port) and
BINARY-PORT? returns #t: what does GET-U8 do?

> Do you know what Industria, Nausicaa, & co. do?

  Nausicaa uses  BINARY-PORT?  and TEXTUAL-PORT?   only when
establishing the conventional class  of a port value; as far
as  I remember  it does  it in  the same  way GOOPS  does to
dispatch multimethods.

  IMHO this R6 statement:

  (textual-port? port) procedure 
  (binary-port? port) procedure 

    The  textual-port?  procedure  returns  #t  if  port  is
    textual,  and  returns  #f otherwise.  The  binary-port?
    procedure returns  #t if port is binary,  and returns #f
    otherwise.

should be enough to derive that:

  (cond ((binary-port? p)
         ---)
        ((textual-port? p)
         ---))

and:

  (cond ((textual-port? p)
         ---)
        ((binary-port? p)
         ---))

must  be  equivalent;  if  they are  not,  confusion  arises
because of violation of the rule of least surprise.

[1] <http://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-9.html#node_sec_8.2.6>
-- 
Marco Maggi