Re: [Haskell-cafe] Is it possible to make lazy combinators for IO?

Urk.. I mean there's no need to execute the readLn action. On Apr 18, 2016 4:18 PM, "David Feuer" <david.feuer@gmail.com> wrote:

If

f :: a -> IO a

for some a, and I want to use

mfix f

then f must not inspect its argument in any way, or the computation will get stuck. In some cases, this seems a bit harsh. For example,

mfix (\x -> fmap (3 :) (x `seq` readLn))

looks perfectly reasonable. There is no need to inspect the return [] action to know that the final result of the computation will begin with 3:. Is there a lazy IO mapping function somewhere that can work such magic?