I'm working on a puzzle solving game in which an exponent function is required, so I define
exp' :: Int -> Int -> Int
exp' = (^)
Here happens the weird:
*Main> exp' 6 25
-8463200117489401856
But
*Main> 6^25
28430288029929701376
I couldn't find any difference between my exp' and (^) from ghci.
Is is a ghc bug?
The Glorious Glasgow Haskell Compilation System, version 8.0.1
I couldn't find any difference
Yes, there are some differences.
:t exp'
exp' :: Int -> Int -> Int
:t (^)
(^) :: (Num a, Integral b) => a -> b -> a
namely
:t (^)
-- Num Integral Num
(^) :: (Num a, Integral b) => a -> b -> a
See? It's about the type.
Simply put, Int is bounded so it can overflow to negative when exceeding allowed range:
> (6::Int) ^ (25::Int)
-8463200117489401856
while Integer is unbounded, so does not overflow:
> (6::Integer) ^ (25::Integer)
28430288029929701376
So, to fix it you just change Int to Integer:
exp' :: Integer -> Integer -> Integer
exp' = (^)
You may want to visit https://www.haskell.org/tutorial/numbers.html for more details about types and Numbers.
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