1 files changed, 71 insertions, 0 deletions
diff --git a/src/Common.hs b/src/Common.hs
new file mode 100644
index 0000000..a196527
--- /dev/null
+++ b/src/Common.hs
@@ -0,0 +1,71 @@
+module Common ((?), (?:), fromDigits, leftPad, listToProse, asOrdinal, showDayOfWeek, showMonth) where
+
+import Data.List (replicate, take)
+import Data.List.NonEmpty (NonEmpty ((:|)))
+import Data.Maybe (fromMaybe)
+import Intro
+
+fromDigits :: [Int] -> Int
+fromDigits = foldl (\n d -> 10 * n + d) 0
+
+leftPad :: Int -> a -> [a] -> [a]
+leftPad m x xs = replicate (m - length ys) x ++ ys
+ where
+  ys = take m xs
+
+(?) :: Bool -> a -> a -> a
+(?) True x _ = x
+(?) False _ y = y
+
+infixr 1 ?
+
+(?:) :: Maybe a -> a -> a
+maybeA ?: b = fromMaybe b maybeA
+
+infixr 0 ?:
+
+listToProse :: NonEmpty String -> String
+listToProse (x :| xs) = mconcat . reverse $ proseJoin xs [x]
+ where
+  proseJoin [] ys = ys
+  proseJoin [y] [] = [y]
+  proseJoin [y] zs = y : " and " : zs
+  proseJoin (y : ys) zs = proseJoin ys (y : ", " : zs)
+
+asOrdinal :: Int -> String
+asOrdinal 11 = "11th"
+asOrdinal 12 = "12th"
+asOrdinal 13 = "13th"
+asOrdinal n =
+  show n ++ case n `mod` 10 of
+    1 -> "st"
+    2 -> "nd"
+    3 -> "rd"
+    _ -> "th"
+
+showDayOfWeek :: Int -> Maybe String
+showDayOfWeek = \case
+  0 -> Just "Sunday"
+  1 -> Just "Monday"
+  2 -> Just "Tuesday"
+  3 -> Just "Wednesday"
+  4 -> Just "Thursday"
+  5 -> Just "Friday"
+  6 -> Just "Saturday"
+  _ -> Nothing
+
+showMonth :: Int -> Maybe String
+showMonth = \case
+  1 -> Just "January"
+  2 -> Just "February"
+  3 -> Just "March"
+  4 -> Just "April"
+  5 -> Just "May"
+  6 -> Just "June"
+  7 -> Just "July"
+  8 -> Just "August"
+  9 -> Just "September"
+  10 -> Just "October"
+  11 -> Just "November"
+  12 -> Just "December"
+  _ -> Nothing