[Haskell-beginners] Absolute beginner's questions...

Barry Burd bburd at drew.edu
Tue Aug 19 14:30:37 EDT 2008

I'm just getting started with Haskell. I've written the following simple program:
module Med
-- lst = [5, 3, 7, 8, 0, 2, 4, 1, 6]
lst = [7, 3, 1, 2, 0, 9, 8]
numLessThan x = length([y | y <- lst, y < x])
numGreaterThan x = length([y | y <- lst, y > x])
median = [ x | x <- lst, numLessThan x == numGreaterThan x]
I realize that this code isn't very robust. My questions are as follows:
- I remember running this code with some values of lst (containing an odd number of unique integer values) and getting the wrong answer. Is that possible? I can't replicate the results because I don't remember what values of lst didn't work.
- How can I add a line or two to display intermediate results (in order to debug the code if necessary)? I've tried adding putTraceMsg but I keep getting parse errors. I probably haven't fully assimilated the syntax of functional programming yet.


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