Add the haskell book

1 files changed, 15 insertions, 0 deletions

diff --git a/Haskell-book/09/src/EnumFromTo.purs b/Haskell-book/09/src/EnumFromTo.purs
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+++ b/Haskell-book/09/src/EnumFromTo.purs
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+module EnumFromTo where
+
+import Data.Array ((:), reverse)
+import Data.Enum (class Enum, succ)
+import Data.Maybe (Maybe(..))
+import Prelude
+
+enumFromTo :: forall a. Enum a => a -> a -> Array a
+enumFromTo start end = reverse $ enumFromTo' [] (Just start)
+    where enumFromTo' :: Array a -> Maybe a -> Array a
+          enumFromTo' acc (Just start')
+              | start' > end  = acc
+              | start' == end = start' : acc
+              | otherwise     = enumFromTo' (start' : acc) (succ start')
+          enumFromTo' acc Nothing = acc