Question

I have a object form this typedef.

type ListDA = (State, [((State, Char), State)], [State])

For a Function, i need the second argument and i don’t now how i get this.

Answer 1

You could write a helper function:

snd3 :: (a, b, c) -> b
snd3 (_, b, _) = b

Or you could do the pattern matching directly in your function parameters, e.g. by replacing

yourFunction object = ...

with

yourFunction object @ (_, secondArgument, _) = ...

You may be better off defining a separate type:

data ListDA = ListDA {firstField  :: State,
                      secondField :: [((State, Char), State)],
                      thirdField  :: [State]}

This method defines accessor functions for you.