Hello Henning, Am Samstag, den 04.12.2010, 12:41 +0100 schrieb Henning Thielemann:
Joachim Breitner schrieb:
Now consider the program:
avg' :: [Int] -> (Int, Int) avg' n = (sum [0..n] `div` length [0..n], length [0..n])
It think this is not typecorrect, since 'n' denotes a list and is used as upper bound in [0..n]. Should it be
avg' ns = (sum ns `div` length ns, length ns)
?
Thanks for noting. The type annotation is wrong. In your case (which I had first), ns is shared and thus would not allow for constant-space calculation of sum and length and would fail to demonstrate my point.
avg n = (sum [0..n] `div` l, l) where l = length [0..n] is safe, because the shared expression (an Int) is smaller than the
I’d say that CSE to thunks and the compiler can tell.
If this is meant to be
avg n = (sum ns `div` l, l) where l = length ns
according to my substitution above, then 'ns' still has to be shared and stored completely.
Right, sorry for the confusion by the wrong type. Greetings, Joachim -- Joachim Breitner e-Mail: mail@joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata@joachim-breitner.de