src/task5/task5.hs

   1 {-# LANGUAGE OverloadedStrings #-}
   2
   3 import Data.Text (Text)
   4 import qualified Data.Text as T
   5 import qualified Data.Text.IO as TIO
   6 import Data.Char (isSpace)
   7
   8
   9 main :: IO ()
  10 main = do
  11         text <- TIO.readFile "data/05-instructions.txt"
  12         let uncommented = deComment text
  13         let expanded = expand uncommented
  14         print $ countNonSpace uncommented
  15         print $ countNonSpace expanded
  16         -- TIO.writeFile "data/05-output.ppm" expanded
  17
  18
  19 countNonSpace :: Text -> Int
  20 countNonSpace = T.length . T.filter (\c -> not (isSpace c))
  21
  22
  23 -- Remove comments
  24 deComment :: Text -> Text
  25 deComment text = deComment' (extractFirstComment text) text
  26
  27 -- If there are no comments, return the text as-is
  28 -- If there is a first comment, decomment the rest
  29 deComment' :: Maybe (Text, Text) -> Text -> Text
  30 deComment' Nothing text = text
  31 deComment' (Just (prefix, suffix)) _ = prefix `T.append` (deComment suffix)
  32
  33 -- Monad notation to string togeether all the Maybes
  34 extractFirstComment :: Text -> Maybe (Text, Text)
  35 extractFirstComment text =
  36     do (prefix, commentSuffix) <- maybeBreakOn "<" text
  37        (_, suffix) <- maybeBreakOn ">" commentSuffix
  38        return (prefix, suffix)
  39
  40
  41 -- Expand compression
  42 expand :: Text -> Text
  43 expand text = expand' (extractFirstExpander text) text
  44
  45 -- If there are no compression markers, return the text
  46 -- If there's one, expand it, and try again.
  47 expand' :: Maybe (Text, Int, Int, Text) -> Text -> Text
  48 expand' Nothing text = text
  49 expand' (Just (prefix, expandLen, expandCount, suffix)) _ =
  50     expand (expandedPrefix `T.append` suffix)
  51     where unexpandedPrefix = T.dropEnd expandLen prefix
  52           group = T.takeEnd expandLen prefix
  53           expanded  = T.replicate expandCount group
  54           expandedPrefix = unexpandedPrefix `T.append` expanded
  55
  56 extractFirstExpander :: Text -> Maybe (Text, Int, Int, Text)
  57 extractFirstExpander text =
  58     do (prefix, suffix) <- maybeBreakOn ":" text
  59        (expanderLenT, suffix') <- maybeBreakOn ":" suffix
  60        (expanderCountT, suffix'') <- maybeBreakOn ":" suffix'
  61        let expanderLen = read $ T.unpack expanderLenT
  62        let expanderCount = read $ T.unpack expanderCountT
  63        return (prefix, expanderLen, expanderCount, suffix'')
  64
  65
  66 -- Uses Text.breakOn, but puts the result in a Maybe
  67 -- Also drops the needle from the returned suffix.
  68 maybeBreakOn :: Text -> Text -> Maybe (Text, Text)
  69 maybeBreakOn needle haystack =
  70     if T.null suffix
  71     then Nothing
  72     else Just (prefix, T.drop (T.length needle) suffix)
  73     where (prefix, suffix) = T.breakOn needle haystack