There is one trick that you might try when you're modifying methods in Base. You can define a new method on the same function. Eg, you can paste the modified method in your terminal:
function Base.sin(x::Float64)
x == 0 && error()
sqrt(1-cos(x)^2)
end
Note that julia might have inlined the old definition, so in some cases you'll
need to restart julia, or rebuild the system image in order for the new
definition to be picked up.
