Add file

src/StringHelp.hs

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+module StringHelp where
+
+--import Data.Char
+
+import Data.Set (Set)
+import qualified Data.Set as Set
+
+isVowel :: Char -> Bool
+isVowel x = case x of
+    'a' -> True
+    'e' -> True
+    'i' -> True
+    'o' -> True
+    'u' -> True
+    _ -> False
+
+addIndefiniteArticle :: String -> String
+addIndefiniteArticle [] = error "tried to add indefinite article to empty string"
+addIndefiniteArticle (x : xs) = genarticle ++ (x : xs)
+  where
+    flipexception
+        | w `Set.member` indefiniteExceptions = not
+        | otherwise = id
+    w = head (words (x : xs))
+    genarticle
+        | flipexception (isVowel x) = "an "
+        | otherwise = "a "
+
+indefiniteExceptions :: Set String
+indefiniteExceptions =
+    Set.fromList
+        [ "one"
+        , "usual"
+        , "union"
+        , "honor"
+        , "honest"
+        , "honorable"
+        , "heir"
+        , "hourglass"
+        , "eulogy"
+        , "united"
+        , "used"
+        ]