Check and reassign the field type

[katat]

There are currently two types of field, either constant or not.

When a variable is declared, it stores and propagate the field type, including the constant value.

The generic function checks uses the constant argument to instantiate the function.

We need to make sure the reassignment of a variable or struct field update the field type accordingly.

[katat]

The type of a struct field is updated when reassignment happens.

But it will still need to take care of the field variable and array variable.