Unfrotunately the answer to this is not simple:
http://stackoverflow.com/questions/4243117/how-to-catch-and-ignore-a-call-to...
'error' more or less terminates the program in an unreasonable way.
It would be preferable for f2 to result in a type that can contain the
error result to be parsed.
Cheers,
Darren
On Oct 31, 2015 21:16, "Roelof Wobben"
Hello,
I have made this exercise which can be found at the Craft of Functional Programming book.
-- exercise 32
-- Suppose we have to raise 2 to the power n. If n is even, 2*m say, then -- 2n = 22*m = (2m)2 -- If n is odd, 2*m+l say, then -- 2n = 22*m+l = (2n)2*2 -- Give a recursive function to compute 2n which uses these insights.
f2 :: Integer -> Integer f2 n | n < 0 = error "This will only run for positive numbers" | n == 0 = 1 | even n = f2 ( n `div` 2) ^ 2 | odd n = (f2 ( n `div` 2) ^ 2) * 2
Now I have to make Hunit tests for it,
But is there a way I can test if the error message is shown when a negative number is being used ?
Roelof
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