Print type after evaluation +t,-t
With the +t option, the interpreter will display both the result
and type of each expression entered at the Hugs prompt:
Prelude> :set +t
Prelude> map (\x -> x*x) [1..10]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100] :: [Int]
Prelude> not True
False :: Bool
Prelude> \x -> x
<> :: a -> a
Prelude>
Note that the interpreter will not display the type of an expression
if its evaluation is interrupted or fails with a run-time error.
In addition, the interpreter will not print the type, IO (), of
a program in the IO monad;
the interpreter treats these as a special case, giving the programmer more
control over the output that is produced.