Question

I have this snippet of a function:

mapM (\x -> do t' <- t; return $ strSwop "if0" ("if" ++ show x) t') [0..(n-1)]

With

strSwop :: String -> String -> String -> String
t :: IO String

It works as expected but I don’t like the IO construct withing the lambda.
How can it be written differently?
I come out of the monad just to be wrapped again next line. Feels ugly.

If I do it this way:

mapM (\x -> t >>= strSwop "if0" ("if" ++ show x) t) [0..(n-1)]

It complains (obviously) about the return signature of strSwop 🙁
strSwop is just a string replacement function.
Is there a way to correctly write this?
Thanks.

— EDIT —

Just figured it out …

Works out:

mapM (\x -> liftM (strSwop "if0" ("if" ++ show x)) t) [0..(n-1)]

Answer 1

I would suggest liftM or <$>

import Control.Applicative
mapM (\x -> strSwop "if0" ("if" ++ show x) <$> t) [0..(n-1)]