Execute HQ9+/Haskell
From Rosetta Code
Execute HQ9+/Haskell is an implementation of HQ9+.
Other implementations of HQ9+.
Execute HQ9+/Haskell is part of RCHQ9+. You may find other members of RCHQ9+ at Category:RCHQ9+.
This HQ9+ interpreter is written in Haskell.
import Char (toLower, toUpper)
main = interact hq9p
hq9p :: String -> String
hq9p source = concatMap run $ map toLower source
where run 'h' = "Hello, world!\n"
run 'q' = source
run '9' = bottles
run _ = ""
-- Obviously, the final case works just fine for '+'.
bottles :: String
bottles = concat
[up (bob n) ++ wall ++ ", " ++ bob n ++ ".\n" ++
pass n ++ bob (n - 1) ++ wall ++ ".\n\n" |
n <- [99, 98 .. 0]]
where bob n = num n ++ " bottle" ++ s n ++ " of beer"
wall = " on the wall"
pass 0 = "Go to the store and buy some more, "
pass _ = "Take one down and pass it around, "
up (x : xs) = toUpper x : xs
num (-1) = "99"
num 0 = "no more"
num n = show n
s 1 = ""
s _ = "s"
