shell-monad-0.6.0: examples/fib.hs

{-# LANGUAGE OverloadedStrings, ExtendedDefaultRules #-}
{-# OPTIONS_GHC -fno-warn-type-defaults #-}
import Control.Monad.Shell
import qualified Data.Text.Lazy as T
import qualified Data.Text.Lazy.IO as T
default (T.Text)

main :: IO ()
main = T.writeFile "fib.sh" $ script $
	takeParameter () >>= fib >>= cmd "echo"

fib :: Term Var Integer -> Script (Term Var Integer)
fib n = do
	prev <- new1
	acc <- new1
	forCmd (cmd "seq" prev n) $ \_ -> do
		setVar acc (val acc + val prev)
		setVar prev (val acc - val prev)
	return acc
  where
	new1 = newVarContaining 1 ()