praxis

commit 3c47ca8f5a6db7d07a8e6f5ac24a8bd8af24c582
parent 690d99a94ea8d9c3fafe97a21fbe5a822e02a26a
Author: Jared Tobin <jared@jtobin.ca>
Date:   Mon,  9 Jul 2018 07:24:37 +1200

Add Floyd's triangle.

Diffstat:
A
20180522_floyd/Floyd.hs
 | 
33
+++++++++++++++++++++++++++++++++

1 file changed, 33 insertions(+), 0 deletions(-)
diff --git a/20180522_floyd/Floyd.hs b/20180522_floyd/Floyd.hs
@@ -0,0 +1,33 @@
+{-# OPTIONS_GHC -Wall #-}
+
+import Data.List as L (unfoldr)
+
+floyd0 :: [[Int]]
+floyd0 = loop 1 [1..] where
+  loop n input =
+    let header = take n input
+        footer = loop (succ n) (drop n input)
+    in  header : footer
+
+floyd1 :: [[Int]]
+floyd1 = L.unfoldr alg (1, 0) where
+  alg (m, n) =
+    let lbound = m
+        ubound = lbound + n
+        range  = [lbound..ubound]
+    in  Just (range, (succ ubound, succ n))
+
+render :: Show a => [a] -> String
+render input = case input of
+  []    -> ""
+  [h]   -> show h
+  (h:t) -> show h ++ " " ++ render t
+
+main :: IO ()
+main = do
+  mapM_ (putStrLn . render) (take 5 floyd0)
+
+  putStrLn ""
+
+  mapM_ (putStrLn . render) (take 5 floyd1)
+