Robert Dockins wrote:
On Sunday 28 May 2006 05:50 pm, you wrote:
[moved to cafe]
Robert Dockins wrote:
On Sunday 28 May 2006 05:02 pm, Brian Hulley wrote:
I see my error was that I was reversing the args in eta expansion,
so the correct derivation is:
FYI, eta-expansions isn't valid in Haskell. Its safe in this
derivation, but it isn't always.
Am I right in thinking that this is because of _|_ ?
Yup. Well, _|_ and seq, really. IIUC, the removal of seq restores the
validity of eta-conversion.
seq _|_ x = _|_
but,
seq (\z -> _|_ z) x = x
Thanks for the illustration. I now recall that Jon Fairbairn wrote in
http://www.haskell.org//pipermail/haskell-cafe/2006-March/015125.html
that seq shouldn't be a function so I suppose this is why.
In any case I suppose I should have instead just replaced the
function with it's definition like you (view Lambda Shell) and
Christophe did.
Also, is your Lambda Shell publicly available? (I had a quick look
on the wiki in the Theorem provers section but couldn't find a link.)
http://www.eecs.tufts.edu/~rdocki01/lambda.html
I've never thought of it as a theorem prover before ;-)
I was just considering any kind of automated derivation to be a proof...
You can also play with it on #haskell via the lambdabot '@lam'
command. I think it binds to a slightly older version, but there
aren't many user-visible changes.
Best regards,
Brian.
--
Logic empowers us and Love gives us purpose.
Yet still the lukewarm dead
try hard
to destroy us.
http://www.metamilk.com
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