Center a triangle (HASKELL) - haskell

Question

Inspired by this question, I have made this code which prints out triangles:
type TriangleMaker = Char -> Int -> [String]
topLeftTriangle :: TriangleMaker
topLeftTriangle c n = [replicate i c | i <- [1 .. n]]
centeredTriangle :: TriangleMaker
centeredTriangle c n = [replicate (n-i) ' ' ++ replicate i c | i <- [0 .. n]]
getType :: IO TriangleMaker
getType = do
let menu = [topLeftTriangle, centeredTriangle]
putStr $ unlines [
"What type of triangle do you want to print? (type 1 and then type the int size)",
"1) Top Left",
"2) Centered"]
line <- getLine
return (menu !! ((read line :: Int) - 1))
trekant :: IO()
trekant = do
triangle <- getType
size <- getLine
putStr $ unlines $ triangle '*' (read size :: Int)
It gives me this output in ghci:
Ok, one module loaded.
ghci> trekant
What type of triangle do you want to print? (type 1 and then type the int size)
1) Top Left
2) Centered
1
6
*
**
***
****
*****
******
ghci> trekant
What type of triangle do you want to print? (type 1 and then type the int size)
1) Top Left
2) Centered
2
6
*
**
***
****
*****
******
I want to make it so that I can use a string as input instead of a char, like so:
trekant :: IO()
trekant = do
triangle <- getType
size <- getLine
putStr $ unlines $ triangle " *" (read size :: Int)
That way, (I think) I'll get a centered triangle as output:
ghci> trekant
What type of triangle do you want to print? (type 1 and then type the int size)
1) Top Left
2) Centered
2
6
*
* *
* * *
* * * *
* * * * *
* * * * * *
Or am I way off here? How can I re-write this so that the triangle is centered?

Answer 1

In case you want to generate a triangle in the center, you should add spaces between two stars, this thus means that the string looks like:
centeredTriangle :: TriangleMaker
centeredTriangle c n = [replicate (n-i) ' ' ++ concat (replicate i [c, ' ']) | i <- [0 .. n]]
We thus generate a string where we have n-i spaces followed by n times the "* " string.
Perhaps it is more elegant to work with intersperse :: a -> [a] -> [a] where we intersperse a list of '*' characters with spaces:
import Data.List(intersperse)
centeredTriangle :: TriangleMaker
centeredTriangle c n = [replicate (n-i) ' ' ++ intersperse ' ' (replicate i c) | i <- [0 .. n]]
This then produces:
ghci> trekant
What type of triangle do you want to print? (type 1 and then type the int size)
1) Top Left
2) Centered
2
6
*
* *
* * *
* * * *
* * * * *
* * * * * *
ghci> trekant
What type of triangle do you want to print? (type 1 and then type the int size)
1) Top Left
2) Centered
2
10
*
* *
* * *
* * * *
* * * * *
* * * * * *
* * * * * * *
* * * * * * * *
* * * * * * * * *
* * * * * * * * * *