References: DRIBBLE (p443)
Edit history: 06-Dec-87, Version 1 by Pitman
14-Feb-88, Version 2 by Masinter
The intent and effect of DRIBBLE is not very clearly specified. Users have
complained that DRIBBLE behaves quite differently in different implementations.
Clarify that DRIBBLE is intended primarily for interactive debugging and that
its effect cannot be relied upon from programs.
#1: (PROGN (DRIBBLE "temp")
#2: (DRIBBLE "temp")
(PROGN (PRINT 'FOO)
Users of DRIBBLE have been surprised about how differently DRIBBLE behaves in
different implementations. This makes the status quo much more explicit and will
lead to less surprise.
Some implementations implement DRIBBLE as a function which simply assigns
streams such as *STANDARD-OUTPUT* to broadcast streams (or the approximate
equivalent thereof). Even within this camp, there is not widespread agreement
about which streams are affected. However, typically test case #1 will capture
the output of (PRINT 'FOO) in the file "temp" and will execute (PRINT 'BAR) but
not capture its output.
Some implementations (eg, Symbolics) push to a recursive command loop when
DRIBBLE is called with an argument, and return from that command loop when
DRIBBLE is called with no argument. In these implementations, test case #1 will
enter a recursive command loop upon the first call to DRIBBLE and will not
execute the (PRINT 'FOO) until (DRIBBLE) is done interactively. When the second
(DRIBBLE) in test case #1 is executed, DRIBBLE will complain that output is not
currently being recorded. In test case #2, the output of (PRINT 'FOO) will be
captured, but the form (PRINT 'BAR) will never be executed because (DRIBBLE)
does not return normally (it throws).
Cost to implementors:
None. This is just a clarification.
Cost to users:
Anyone who currently uses DRIBBLE in code that is believed to be portable is
kidding himself. If such code works in some implementations, it can continue to
Users will be aware that they cannot rely on DRIBBLE in portable code.
No apparent effect.
DRIBBLE, like other environment features, is a standard interface to a
non-standard feature. As such, there is some question as to its place in the
ANSI standard. However, if DRIBBLE remains in the standard, its behavior is made
explicitly vague by this proposal.