Execute HQ9+/Haskell

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. We use mapAccumR to maintain the accumulator. However, the specification doesn't say what to do with said accumulator on completion. <lang haskell>module Main where

import Data.Char (toLower, toUpper) import Data.List -- for concat import Data.Traversable -- for mapAccumR

main :: IO () main = do

 s <- getLine
 putStrLn (snd (hq9p s))

hq9p :: String -> (Int,String) hq9p src = fin $ mapAccumR run 0 $ map toLower src

 where
   fin (acc,log) = (acc,concat log)
   run acc ch = case ch of
     'h' -> (acc,"Hello, world!")
     'q' -> (acc,src)
     '9' -> (acc,bottles)
     '+' -> (acc + 1,"")
     '_' -> (acc,"")

bottles :: String bottles = [99, 98 .. 0] >>= beers

 where
   beers n = unlines [
     bob n ++ " on the wall, " ++ bob n ++ ".",
     pass n ++ bob (n - 1) ++ " on the wall.\n"]
   bob n =
     let nu = case n of { (-1) -> "99"; 0 -> "No more"; n -> show n; }
         s  = if n == 1 then "" else "s"
     in nu ++ " bottle" ++ s ++ " of beer"
   pass n = case n of
     0 -> "Go to the store and buy some more, "
     _ -> "Take one down and pass it around, "</lang>