Subject: Re: function ports?
From: (Rob Warnock)
Date: 1999/07/08
Newsgroups: comp.lang.scheme
Message-ID: <7m38l2$>
Dirk Herrmann  <> wrote:
| Is there an implementation of scheme that supports in addition to file
| and string ports something like function ports?  For example:
| (open-input-function 
|   (lambda () 
|     (<some code that returns characters or strings>)))

Yes, several implementations -- e.g., MzScheme, SCM, to name just two --
provide "custom" or "soft" ports (their respective names), for which
the basic actions on ports (e.g., read-char, char-ready?, close etc.)
are provided by the user as Scheme procedures when creating the port.
For Mzscheme, the interface is:

	(make-input-port getc-proc char-ready?-proc close-proc)
	(make-output-port write-string-proc close-proc)

And for SCM:

	(make-soft-port a-vector-of-procs IO-modes)
	  where the elements [not all are needed] of the vector are:
	  0 procedure accepting one character for output
	  1 procedure accepting a string for output
	  2 thunk for flushing output
	  3 thunk for getting one character
	  4 thunk for closing port (not by garbage collection)


Rob Warnock, 8L-855
Applied Networking
Silicon Graphics, Inc.		Phone: 650-933-1673
1600 Amphitheatre Pkwy.		FAX: 650-933-0511
Mountain View, CA  94043	PP-ASEL-IA