Dirk Herrmann  <Herrmann@ida.ing.tu-bs.de> 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

-----
Rob Warnock, 8L-855		rpw3@sgi.com
Applied Networking		http://reality.sgi.com/rpw3/
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