On Apr 5, 2006, at 12:42 PM, Josef Svenningsson wrote:
Sorry to barge in in the middle of your discussion here..
Hey, if we wanted a private conversation, we'd take it off-list. :-)
On 4/5/06, Robert Dockins <[EMAIL PROTECTED]> wrote:
There is a fair bit of disagreement about what referential
transparency means. I found the following link after googling around
a bit; it seems to address some of these issues.
http://www.cs.indiana.edu/~sabry/papers/purelyFunctional.ps
Do you have any reference to the fact that there is any diagreement
about the term? I know it has been used sloppily at times but I think
it is pretty well defined. See section 4 of the following paper:
http://www.dina.kvl.dk/~sestoft/papers/SondergaardSestoft1990.pdf
http://en.wikipedia.org/wiki/Referential_transparency
http://lambda-the-ultimate.org/node/1237
It may be that experts have a well defined notion of what it means,
but I think that non-experts (ie, most people) have a pretty vague
idea of exactly what it means.
Readers digest:
First we need a denotational semantics and a corresponding equality
which I call '='. A language is then referentially transparent if for
all expressions e,e1 and e2, if e1 = e2 then e[x:=e1] = e[x:=e2].
Here e[x:=e'] denotes substitution where the variable x is replaced
with e' in the expression e.
So it's a standard substitutivity property. The only problem here is
that Haskell has a pretty hairy denotational semantics and I don't
think anyone has spelled it out in detail.
I think that may be the main problem, at least in this context. We
can take a nice lovely definition of rt, as above, but its
meaningless without a good semantic model. So we're forced to
approximate and hand-wave, which is where the disagreement comes in.
The thing which I think
comes closest is the following paper which investigates the
denotational implications of have seq as a primitive:
http://www.crab.rutgers.edu/~pjohann/seqFinal.pdf
Cheers,
/Josef
Thanks for these paper links; I'll be reading them as soon as I find
a few moments.
Rob Dockins
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
-- TMBG
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