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Welcome to the Fibonacci in Haskell page! Here, you’ll find the source code for this program as well as a description of how the program works.
module Main where
import System.Environment
import Text.Read
fibonacci :: Int -> [Integer]
fibonacci = flip (take) fibs
fibs :: [Integer]
fibs = 1 : 1 : zipWith (+) fibs (tail fibs)
headMaybe :: [a] -> Maybe a
headMaybe [] = Nothing
headMaybe (x:xs) = Just x
-- Takes a list of values and returns a list of strings in the format "ONE_BASED_INDEX: VALUE"
printWithIndex :: (Show a) => [a] -> [[Char]]
printWithIndex = zipWith (\i x -> (show i) ++ ": " ++ (show x)) [1..]
-- Prints out the first N numbers from the fibonacci sequence
-- where N equals to the first command line argument.
main :: IO ()
main = do
args <- getArgs
let n = headMaybe args
case n >>= readMaybe of
Nothing -> putStrLn "Usage: please input the count of fibonacci numbers to output"
Just n -> mapM_ (putStrLn) $ (printWithIndex . fibonacci) n
Fibonacci in Haskell was written by:
If you see anything you’d like to change or update, please consider contributing.
Note: The solution shown above is the current solution in the Sample Programs repository as of Apr 07 2019 00:40:32. The solution was first committed on Oct 15 2018 18:50:33. As a result, documentation below may be outdated.
No ‘How to Implement the Solution’ section available. Please consider contributing.
No ‘How to Run the Solution’ section available. Please consider contributing.