Refinement type predicate does not support functions and operators

[jlvargasme]

Issue description:

let pi = 3.14159 let y0 : int{ -y0 >= pi} = 4.0

Will compile successfully because (-y0) is interpreted as "42". The dummy value we use when there is no handling.

Action: Implement operator and function application checks inside refinement variable declaration.

[jlvargasme]

Fixed by implementing unary minus