[r6rs-discuss] [Formal] allow port position to be "magic cookie"

[Per Bothner]

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Type of issue: Enhancement
Priority: Minor
Component: I/O
Version: 5.92

port-position and set-port-position! are specified to get/set the
port's current position as a byte offset.  But there are many kinds
of ports which do have a position, and on which the position can be
changed, but not using a byte offset.  This includes most text ports
(except those implemented using simple stateless transcoders).
In some cases a character offset may make more sense.

Suggestion: For non-binary ports allow the use of any arbitrary
integral "magic cookie" as the position.  One could also allow
an arbitrary value (such as a record), though that reduces the
"typeability" of these procedures.  However, that would allow
a straight-forward wrapping of  C's fgetpos/fsetpos.
-- 
	--Per Bothner
per at bothner.com   http://per.bothner.com/