On Thu, Jun 11, 2009 at 4:26 PM, Felipe Lessa
On Thu, Jun 11, 2009 at 04:14:22PM -0400, David Menendez wrote:
Aside from assertions that this is a bad thing because you say so, what evidence do we have that this is a problem?
The wiki mentions the problem with forgetting the results of an operation.
This is exactly what I'm talking about. That page is written almost entirely by Henning Thielemann, but because it's on the official Haskell wiki, it seems authoritative.
Another problem is using functions that needlessly produce results because you're interested in the side effects only. For example,
do mapM something1 list something2
I do agree that someone is less likely to accidently write do ignore (mapM something1 list) something2 But this is generally less dangerous than, say, using foldl instead of foldl'.
(Hmmm, would something like
{-# RULES "mapM/mapM_" mapM = mapM_ #-}
work nicely?)
Unfortunately, I don't think that rule would ever be applied, because
the types of mapM and mapM_ don't match.
You could have a rule that transformed ignore (mapM x y) to mapM_ x y, though.
--
Dave Menendez