Simplest way to mix anonymous conditions with IO

Question

How to avoid boilerplate assignments like doesExist <- doesDirectoryExist path and case doesExist of ... within IO?

Is there a more idiomatic way than this?

import System.Directory import System.Environment main = do path:_ <- getArgs doesDirectoryExist path >>= cond (putStrLn $ path ++ " Exists") (putStrLn $ path ++ " Does not exist") cond b c a = if a then b else c

BTW, cond is flip bool if you import Data.Bool.

chi
– chi

2015-02-14 13:13:38 +00:00
Commented Feb 14, 2015 at 13:13 — chi
– chi, Commented Feb 14, 2015 at 13:13

András Kovács · Accepted Answer · 2015-02-14 13:08:10Z

LambdaCase is applicable here:

{-# LANGUAGE LambdaCase #-} import System.Directory import System.Environment main = do path:_ <- getArgs doesDirectoryExist path >>= \case True -> putStrLn $ path ++ " Exists" _ -> putStrLn $ path ++ " Does not exist"

dfeuer · Accepted Answer · 2015-02-14 14:08:42Z

0

Or same with "if":

doesDirectoryExist path >>= \x -> if x then (putStrLn "Exists") else putStrLn ("Does not")

edited Feb 14, 2015 at 14:08

dfeuer

48.8k5 gold badges69 silver badges171 bronze badges

answered Feb 14, 2015 at 13:35

Izabel

3012 silver badges2 bronze badges

Collectives™ on Stack Overflow

Simplest way to mix anonymous conditions with IO

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related