initial commit

README.md

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+# allArgsAdd
+
+A simple program to add all arguments.
+
+Built to explore & implement folding over Monads.
+
+## Build
+
+`ghc allArgsAdd.hs`

allArgsAdd.hs

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+module Main where
+import System.Environment
+import Text.Read
+
+main :: IO ()
+main = do
+  args <- getArgs
+  case (foldMaybeNum [readMaybe s :: Maybe Double | s <- args]) of
+    (Just n) -> roundMaybe n
+    Nothing -> putStrLn "Those weren't numbers!"
+
+foldMaybeNum :: (Num a, Eq a) => [Maybe a] -> Maybe a
+foldMaybeNum x = foldr (\a b -> (+) <$> a <*> b) (Just 0) x
+
+-- Decide whether to print the double as an int, or a double
+roundMaybe :: Double -> IO ()
+roundMaybe n =
+  if n == fromInteger (round n) then
+    (putStrLn . show) (round n :: Integer)
+  else (putStrLn . show) n