Haskell Debugging
functional-programming, haskell
Solution
For debugging, there's
import Debug.Trace
funct :: Integer -> [Integer] -> Bool
funct a list = trace (show list) $ funct (a + 1) (a : list)
where `trace :: String -> a -> a`. It uses `unsafePerformIO` under the hood, so it's evil and only for debugging.
Be aware that due to lazy evaluation, the debugging output may appear in surprising order and interleaved with the output the program would normally generate.
With
module TraceIt where
import Debug.Trace
funct :: Integer -> [Integer] -> Bool
funct 10 list = null list
funct a list = trace (show list) $ funct (a + 1) (a : list)
I get
*TraceIt> funct 1 []
[]
[1]
[2,1]
[3,2,1]
[4,3,2,1]
[5,4,3,2,1]
[6,5,4,3,2,1]
[7,6,5,4,3,2,1]
[8,7,6,5,4,3,2,1]
False
as expected.
Problem
How can I print a list or something in haskell at every call for example : ``` funct a list = funct (a + 1) (a : list) print list here ??????? but how ? ```