feat(hst): :star:HEADmaster

2 files changed, 34 insertions, 0 deletions

diff --git a/template/src/exe/Main.hs b/template/src/exe/Main.hs
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+++ b/template/src/exe/Main.hs
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+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Main where
+
+import           System.Environment             ( getArgs )
+import           Template                       ( fib )
+
+main :: IO ()
+main = do
+  -- https://lotz84.github.io/haskellbyexample/ex/command-line-arguments
+  args <- getArgs
+  let arg = head args
+
+  -- https://stackoverflow.com/a/20667721
+  print (fib (read arg :: Int))
diff --git a/template/src/lib/Template.hs b/template/src/lib/Template.hs
new file mode 100644
index 0000000..29103b2
--- /dev/null
+++ b/template/src/lib/Template.hs
@@ -0,0 +1,19 @@
+module Template
+  ( fib
+  ) where
+
+import           Data.Bits
+import           Data.List
+
+-- https://wiki.haskell.org/The_Fibonacci_sequence
+fib :: Int -> Integer
+fib n =
+  snd
+    . foldl_ fib_ (1, 0)
+    . dropWhile not
+    $ [ testBit n k | k <- let s = bitSize n in [s - 1, s - 2 .. 0] ]
+ where
+  fib_ (f, g) p | p         = (f * (f + 2 * g), ss)
+                | otherwise = (ss, g * (2 * f - g))
+    where ss = f * f + g * g
+  foldl_ = foldl' -- '