On Dec 7, 2005, at 12:05 PM, Simon Marlow wrote:
On 07 December 2005 16:38, Malcolm Wallace wrote:
"Simon Marlow" <[EMAIL PROTECTED]> writes:
I should have said that if 'acts' blocks, then the transformation is
invalid.
Well that is exactly what I was assuming when I said that the
transformation is invalid. In the general case, for some arbitrary
actions between the write and the read (excluding another write of
course), there is no guarantee that the IORef remains unmodified.
This is an analysis that's performed all the time in C compilers, it's
quite straightforward to do a good approximation. One simple
algorithm
is: a store can be forwarded to a matching read as long as there
are no
intervening writes that may alias, or function calls.
C does this and C has threads, so what's the difference?
I would personally be very uncomfortable justifying a semantic
transformation based on common practice in C compilers. What exactly
are the semantics of C programs and why do we believe that C
compilers are correct?
I'd much rather see some argument in terms of an appropriate
definition of observational equivalence.
[snip]
Rob Dockins
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