Haskell variant for day seven

day-07-haskell/app/Main.hs

@@ -0,0 +1,35 @@
+module Main (main) where
+
+import System.Environment.Blank ( getArgs )
+import Common
+import Task1 (task1)
+import Task2 (task2)
+
+main :: IO ()
+main = do
+  args <- getArgs
+  case args of
+    ["1", file] -> do
+      equations <- readEquationsFromFile file
+      print $ task1 equations
+    ["2", file] -> do
+      equations <- readEquationsFromFile file
+      print $ task2 equations
+    _ -> error "Usage: <1|2> <input file>"
+
+readEquationsFromFile :: String -> IO [Equation]
+readEquationsFromFile file = do
+  content <- readFile file
+  return $ map parseLine $ lines content
+
+parseLine :: String -> Equation
+parseLine line = fromWords $ words line
+  where
+    fromWords :: [String] -> Equation
+    fromWords (firstWord:args) = (read $ reverse $ dropFirst $ reverse firstWord, map read args)
+      where
+        dropFirst :: String -> String
+        dropFirst (_:xs) = xs
+        dropFirst x = x
+    fromWords parts = error $ "Illegal line: " ++ unwords parts
+