Question

this is a really basic question I know, I am a begginer in Haskell. So, I am wondering how to “take” the lists from a function like:

putStr( f [[1,2,3],[4,5,6],[6,7,8]])

I don’t know if I am expressing this correctly, but I want to create a function f that takes this type:

type Matrix a = [[a]]
type IntMat = Matrix Integer

and then does some things on each “row” of the matrix, nameley the inner lists.

The thing is, I am not quite sure as to how to address them! :S
If I am not making ANY sense at all, please ask me to explain!

Thank you in advance!

Answer 1

“find the max of each of the inner lists”, “find their length to use later on”, both of them can be done with the map higher-order function.

Prelude> let a = [[1,2,3],[4,5,6],[6,7,8]] :: [[Integer]]
Prelude> map maximum a
[3,6,8]
Prelude> map length a
[3,3,3]

If you have a list M = [a, b, c, d, ...], and you want to use a function f to transform the list into N = [f(a), f(b), f(c), f(d), ...], then you could use the function map (N == map f M).