Question

How can I write a function in Haskell, that takes an input string in the format a1a2a3 and expands into a1a2a2a3a3a3. For example input string “code” would be expanded into “coodddeeee”

Answer 1

Probably very inefficient 🙂

f :: Int -> [Char] -> [Char]
f _ [] = []
f n (c:s) = (replicate n c) ++ (f (n+1) s)

g :: [Char] -> [Char]
g s = f 1 s

.

*Main> g "code"
"coodddeeee"