X-Git-Url: https://git.njae.me.uk/?p=advent-of-code-20.git;a=blobdiff_plain;f=advent18%2Fsrc%2Fadvent18.hs;fp=advent18%2Fsrc%2Fadvent18.hs;h=1ee07f57dc82b7c0e57565289fb96159f8054c04;hp=0000000000000000000000000000000000000000;hb=ff7c977aec28eed475a009d86e7f5d2b63de672f;hpb=b49dd731ff412a5f60fa70f0d288fe532c3b55e6

diff --git a/advent18/src/advent18.hs b/advent18/src/advent18.hs
new file mode 100644
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+++ b/advent18/src/advent18.hs
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+-- import Debug.Trace
+
+import Data.Text (Text)
+-- import qualified Data.Text as T
+import qualified Data.Text.IO as TIO
+
+import Data.Attoparsec.Text hiding (take)
+-- import Data.Attoparsec.Combinator
+import Control.Applicative
+-- import Control.Applicative.Combinators
+
+data Expression 
+  = Number Integer
+  | Mul Expression Expression
+  | Add Expression Expression
+  deriving (Show, Eq)
+
+
+main :: IO ()
+main = 
+  do  text <- TIO.readFile "data/advent18.txt"
+      print $ part1 text
+      print $ part2 text
+
+
+part1 = parseAndEval expressionsP
+part2 = parseAndEval pExpressionsP
+
+parseAndEval parser text = sumEval $ successfulParse parser text
+
+sumEval = sum . map evaluate
+
+showE (Number x) = show x
+showE (Mul a b) = "(" ++ showE a ++ " * " ++ showE b ++ ")"
+showE (Add a b) = "(" ++ showE a ++ " + " ++ showE b ++ ")"
+
+evaluate (Number x)  = x
+evaluate (Mul a b) = (evaluate a) * (evaluate b)
+evaluate (Add a b) = (evaluate a) + (evaluate b)
+
+
+-- Parse the input file
+
+numberP = Number <$> decimal
+mulExprP = string " * " *> pure Mul
+addExprP = string " + " *> pure Add
+
+
+-- Part 1 parsing
+
+expressionsP = exprP `sepBy` endOfLine
+
+exprP = elementP `chainl1` (mulExprP <|> addExprP)
+
+elementP = numberP <|> bracketedP
+bracketedP = "(" *> exprP <* ")"
+
+
+-- Part 2 parsing
+
+pExpressionsP = pExprP `sepBy` endOfLine
+
+pExprP = pTermP `chainl1` mulExprP
+pTermP = pElementP `chainl1` addExprP
+
+pElementP = numberP <|> pBracketedP
+pBracketedP = "(" *> pExprP <* ")"
+
+
+-- chainl1 :: Parser a -> Parser (a -> a -> a) -> Parser a
+-- chainl1 p op = p >>= rest
+--     where 
+--         rest a = (do
+--             f <- op
+--             b <- p
+--             rest (f a b)) <|> pure a
+
+
+chainl1 :: Parser a -> Parser (a -> a -> a) -> Parser a
+p `chainl1` op = do a <- p
+                    rest a
+  where rest a = (do f <- op
+                     b <- p
+                     rest (f a b))
+                 <|> return a
+
+
+-- successfulParse :: Text -> (Integer, [Maybe Integer])
+successfulParse parser input = 
+  case parseOnly parser input of
+    Left  _err -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
+    Right expressions -> expressions