Create reader for evaluable type

[devcdcc]

The Evaluable type must complain for computable values or functions, i.e.
computable value:

{
a = 22
a  ^ 2 // return
}

// or 
 => // evaluate if that syntax or something similar does make sense.
    a = 22
    a ^ 2

the function is similar to the behind code, but it will work as a lambda, meaning that could be computable many times and could receive parameters.
Example:

(a,b) = (a + b) ^ 2


// or

(a, b)  =
    c = a + b
    c ^ 2

// parameters also could be typed 
(a; U, b: U) =
    c = a + b
    c ^ 2

// or typed params with return type
(a; U, b: U) => F[U] =
    c = a + b
    c ^ 2

[devcdcc]

it should be merged with #2.