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Sequence points, undefined behaviour

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From:
Nicholas Clark
Date:
September 10, 2005 04:22
Subject:
Sequence points, undefined behaviour
Message ID:
20050910112229.GB25158@plum.flirble.org
I might have missed this somewhere in the documentation, but is Perl 6 going
to have any documented notion of things like sequence points, undefined
behaviour, etc? Is it going to mandate that function arguments are evaluated
in any particular order (eg left to right)? Is it going to fix the behaviour
if you modify a variable more than once in an expression?

Currently Perl 5 makes no written guarantees on many things, yet everyone has
come to expect the current implementation's choices to be the way things must
be. Is Perl 6 going to do the same, or will it be an explicit goal that
anyone can implement a clean room Perl 6 compiler/runtime with only the
written spec, without needing to match specific case behaviour encoded
solely in regression tests?

Perl 5 is also lets C's undefined behaviour poke through to the language level.
Should Perl 6 avoid this completely? What's 1 << -1 in Perl 6?

Nicholas Clark

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