Implement Day 1

.gitignore

+*.template
+*.cabal
+dist
+dist-*
+cabal-dev
+*.o
+*.hi
+*.chi
+*.chs.h
+*.dyn_o
+*.dyn_hi
+.hpc
+.hsenv
+.cabal-sandbox/
+cabal.sandbox.config
+*.prof
+*.aux
+*.hp
+*.eventlog
+.stack-work/
+cabal.project.local
+cabal.project.local~
+.HTF/
+.ghc.environment.*
+.vscode

input/day01

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package.yaml

+name: advent-of-code
+license: Apache-2.0
+git: "https://git.eisfunke.com/research/advent-of-code-2019"
+author: "Nicolas Lenz"
+maintainer: "nicolas@eisfunke.com"
+
+dependencies:
+- base
+- classy-prelude
+- text
+- megaparsec
+
+default-extensions:
+- NoImplicitPrelude
+- OverloadedStrings
+- LambdaCase
+
+executables:
+  advent-of-code:
+    main: main.hs
+    source-dirs: src
+    ghc-options:
+    - -Wall
+    - -O2
+    - -threaded
+    - -rtsopts
+    - -with-rtsopts=-N

src/Day01.hs

+module Day01 (part1, part2) where
+
+import ClassyPrelude
+import Text.Read
+
+part1, part2 :: [Text] -> Int
+part1 = sum . map (fuel . (read :: String -> Int) . unpack)
+part2 = sum . map (fuelRecursive . (read :: String -> Int) . unpack)
+
+fuel :: Int -> Int
+fuel = (max 0) . (subtract 2) . (`div` 3)
+
+fuelRecursive :: Int -> Int
+fuelRecursive 0 = 0
+fuelRecursive mass = fuel mass + fuelRecursive (fuel mass)

src/main.hs

+import ClassyPrelude
+import Day01
+
+main :: IO ()
+main = getArgs >>= \case
+    [day, part] -> do
+        input <- lines <$> (readFileUtf8 . unpack $ "input/day" <> day)
+        putStrLn $ case lookup (day, part) solutions of
+            Just f -> "Result " <> day <> "-" <> part <> ": " <> f input
+            Nothing -> "Incorrect arguments."
+    _ -> putStrLn "Incorrect arguments."
+
+solutions :: [( (Text, Text), [Text] -> Text )]
+solutions =
+    [ ( ("01", "1"), tshow . Day01.part1 )
+    , ( ("01", "2"), tshow . Day01.part2 )
+    ]

stack.yaml

+resolver: lts-14.16

stack.yaml.lock

+# This file was autogenerated by Stack.
+# You should not edit this file by hand.
+# For more information, please see the documentation at:
+#   https://docs.haskellstack.org/en/stable/lock_files
+
+packages: []
+snapshots:
+- completed:
+    size: 524804
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/14/16.yaml
+    sha256: 4d1519a4372d051d47a5eae2241cf3fb54e113d7475f89707ddb6ec06add2888
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