I just learned about Maybe in Haskell, so I decided to try to use it with a binary search.
Here's the function:
binarySearch :: (Ord a, Int b) => [a] -> a -> b -> b -> Maybe b
binarySearch l e beg last
| lookat < e = (binarySearch l e i last)
| lookat > e = (binarySearch l e beg i)
| lookat == e = Just i
| otherwise = Nothing
where i = floor ((beg+last)/2)
lookat = l !! i
l is a list, e is the element of interest, beg is the start of
the section of interest and end is the end of said section. The error I am getting is:
BinarySearch.hs:1:25:
`Int' is applied to too many type arguments
In the type signature for `binarySearch':
binarySearch :: (Ord a, Int b) => [a] -> a -> b -> b -> Maybe b
I have tried a few other things including:
binarySearch :: Ord a => [a] -> a -> Int -> Int -> Maybe b
Yielding the error:
BinarySearch.hs:6:23:
Could not deduce (b ~ Int)
from the context (Ord a)
bound by the type signature for
binarySearch :: Ord a => [a] -> a -> Int -> Int -> Maybe b
at BinarySearch.hs:(3,1)-(9,22)
`b' is a rigid type variable bound by
the type signature for
binarySearch :: Ord a => [a] -> a -> Int -> Int -> Maybe b
at BinarySearch.hs:3:1
In the first argument of `Just', namely `i'
In the expression: Just i
In an equation for `binarySearch':
binarySearch l e beg last
| lookat < e = (binarySearch l e i last)
| lookat > e = (binarySearch l e beg i)
| lookat == e = Just i
| otherwise = Nothing
where
i = floor ((beg + last) / 2)
lookat = l !! i
I am not sure what I am doing wrong. Any corrections or comments on style or solution would be highly appreciated.
