Haskell Debugging

Haskell code can be debugged using Debug.Trace (trace), to show the evaluation of variables for each call of a function.

trace is inserted in the function with the following syntax

<function name> = trace (<string to display on evaluation>) (<function body>)

Examples

import Debug.Trace (trace)
 
(^) :: Int -> Int
:{
m ^ 0 = 1
m ^ n = trace (show m ++ "^" ++ show n) (m * (m ^ (n-1)))
:}
 
2^3

2^3 2^2 2^1 8