Is Haskell truly pure (is any language that deals with input and output outside the system)?

Question

After touching on Monads in respect to functional programming, does the feature actually make a language pure, or is it just another \"get out of jail free card\" for reason

Answer 1

Is Haskell truly pure? [...]

The Haskell language was pure; the last version being Haskell 1.2. Back then, the type of main was:

main :: [Response] -> [Request]

which was usually abbreviated to:

main :: Dialogue

where:

type Dialogue = [Response] -> [Request]

and Response along with Request were humble, albeit large datatypes:

The advent of I/O using the monadic interface in Haskell changed all that - no more visible datatypes, just an abstract specification. As a result, how IO, return, (>>=) etc are defined is now specific to each implementation of Haskell.

So the question is now:

• is I/O in your implementation of Haskell pure?

As Owen Stephens notes in Approaches to Functional I/O:

I/O is not a particularly active area of research, but new approaches are still being discovered [...]

The Haskell language may once again have a pure, fully-defined model for I/O...