On Mon, Sep 9, 2013 at 7:26 PM, Bryan Vicknair
Deep in a WAI web app, I have a function that converts a String from a web form like "0.12" to an Int 12. Converting "0.12" to the Float 0.12 is working. However, converting the Float 0.12 to the Int 12 does not work as expected unless I use the trace function.
In the following, f = 0.12::Float, gotten from a function that parses "0.12" into 0.12.
In the following expression, the result is: Success (Just 11).
Success $ Just $ truncate (f * 100)
In the following expression, the result is: Success (Just 12)
let expanded = f * 100 ans = truncate expanded in trace (show expanded) $ Success $ Just $ ans
That made me think that "f * 100" had to be strictly evaluated before given to truncate for some reason, so I tried using seq to get the same effect, but that didn't work. Am I correct in assuming that laziness has something to do with this problem?
It would be a serious bug if that was true since lazyness shouldn't change the semantic of a program, except sometimes by allowing the program to terminate where the strict version wouldn't. On the other hand I can't reproduce your bug, couldn't you provide more details (including GHC version and parsing code) -- Jedaï