You have declared (well, described, but by type inference that's the same thing) main to take a parameter of type "unit" (empty tuple). main doesn't take parameters.

Haskell parameters do not work the way most common languages do; using parentheses in function calls the way you would in C/Java/Python etc. will generally get you unexpected type errors, because you're telling it you're passing tuples around. So, the function call

    f()    (f :: () -> a)

is different from

    f    (f :: a)

and the function call

    f(a, b)    (f :: (a,b) -> c)

is different from

    f a b    (f :: a -> b -> c)

(The inferred type of `f` is shown after each call.)

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