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
  17
  18 countNonSpace :: Text -> Int
  19 countNonSpace = T.length . T.filter (\c -> not (isSpace c))
  20
  21
  22 -- Remove comments
  23 deComment :: Text -> Text
  24 deComment text = deComment' (extractFirstComment text) text
  25
  26 -- If there are no comments, return the text as-is
  27 -- If there is a first comment, decomment the rest
  28 deComment' :: Maybe (Text, Text) -> Text -> Text
  29 deComment' Nothing text = text
  30 deComment' (Just (prefix, suffix)) _ = prefix `T.append` (deComment suffix)
  31
  32 -- Monad notation to string togeether all the Maybes
  33 extractFirstComment :: Text -> Maybe (Text, Text)
  34 extractFirstComment text =
  35     do (prefix, commentSuffix) <- maybeBreakOn "<" text
  36        (_, suffix) <- maybeBreakOn ">" commentSuffix
  37        return (prefix, suffix)
  38
  39
  40 -- Expand compression
  41 expand :: Text -> Text
  42 expand text = expand' (extractFirstExpander text) text
  43
  44 -- If there are no compression markers, return the text
  45 -- If there's one, expand it, and try again.
  46 expand' :: Maybe (Text, Int, Int, Text) -> Text -> Text
  47 expand' Nothing text = text
  48 expand' (Just (prefix, expandLen, expandCount, suffix)) _ =
  49     expand (expandedPrefix `T.append` suffix)
  50     where unexpandedPrefix = T.dropEnd expandLen prefix
  51           group = T.takeEnd expandLen prefix
  52           expanded  = T.replicate expandCount group
  53           expandedPrefix = unexpandedPrefix `T.append` expanded
  54
  55 extractFirstExpander :: Text -> Maybe (Text, Int, Int, Text)
  56 extractFirstExpander text =
  57     do (prefix, suffix) <- maybeBreakOn ":" text
  58        (expanderLenT, suffix') <- maybeBreakOn ":" suffix
  59        (expanderCountT, suffix'') <- maybeBreakOn ":" suffix'
  60        let expanderLen = read $ T.unpack expanderLenT
  61        let expanderCount = read $ T.unpack expanderCountT
  62        return (prefix, expanderLen, expanderCount, suffix'')
  63
  64
  65 -- Uses Text.breakOn, but puts the result in a Maybe
  66 -- Also drops the needle from the returned suffix.
  67 maybeBreakOn :: Text -> Text -> Maybe (Text, Text)
  68 maybeBreakOn needle haystack =
  69     if T.null suffix
  70     then Nothing
  71     else Just (prefix, T.drop (T.length needle) suffix)
  72     where (prefix, suffix) = T.breakOn needle haystack