Add the haskell book

1 files changed, 27 insertions, 0 deletions

diff --git a/Haskell-book/09/src/Exercises.purs b/Haskell-book/09/src/Exercises.purs
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+module Exercises where
+
+import Data.Array (filter)
+import Data.Char (toLower, toUpper)
+import Data.Maybe (Maybe(..))
+import Data.String (fromCharArray, toCharArray, uncons)
+import Prelude
+
+-- 2
+filterUppercase :: String -> String
+filterUppercase s = fromCharArray $ filter (\x -> toLower x /= x) (toCharArray s)
+
+-- 3
+capitalize :: String -> String
+capitalize s = maybeCapitalize $ uncons s
+  where maybeCapitalize Nothing = ""
+        maybeCapitalize (Just {head, tail}) = (fromCharArray $ [ toUpper head ]) <> tail
+
+-- 4
+capitalize' :: String -> String
+capitalize' s = fromCharArray $ map toUpper $ toCharArray s
+
+-- 5
+firstLetter :: String -> Maybe Char
+firstLetter = firstLetter' <<< uncons
+  where firstLetter' Nothing = Nothing
+        firstLetter' (Just {head, tail}) = Just $ toUpper head