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Re: binary-port?

From: Ludovic Courtès
Subject: Re: binary-port?
Date: Tue, 26 Apr 2011 17:00:32 +0200
User-agent: Gnus/5.110015 (No Gnus v0.15) Emacs/23.3 (gnu/linux)

Hi Andreas,

Andreas Rottmann <address@hidden> writes:

> Well, I'm not advocating making them disjoint in the sense that the
> textual or binary operations are only possible on "matching" ports.
> Allowing to mix binary and textual I/O on any port, is, IMHO, a fine and
> reasonable implementation-specific extension that Guile provides.  What
> I'm after is making `textual-port?' and `binary-port?' establish a
> partition on the set of possible ports; i.e.
> (textual-port? X) = (not (binary-port? X))
> for any port X (or at least for any port obtainable via R6RS-specified
> procedures).  For that to work, we somehow need to distinguish between
> Latin-1 ports and "pure" binary ports.  Perhaps by adding a flag
> indicating this to the port objects?  This flag would then be set by all
> R6RS procedures specified to create binary ports, and would be checked
> by `binary-port?' and `textual-port?'.  Additionally, we might want to
> clear that flag when the port's encoding is changed to non-#f.  WDYT?

I think we could just as well change ‘textual-port?’ to

  (define (textual-port? p) (not (binary-port? p)))

So you would have the illusion of disjoint types, with the important
difference that:

  1. All I/O operations can be used on all ports.

  2. Using textual operations or ‘set-encoding!’ irreversibly makes a
     port pass ‘textual-port?’ if it didn’t already.



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