Detect pre-existing variables.

[GiggleLiu]

forbid x ← expr if x is already defined in the local scope.

[GiggleLiu]

julia> using NiLang

julia> @i function f(x)
           y ← 0
       end

julia> @i function f(x)
           x ← 0  # if left side is already defined, should error
       end

@thautwarm , the second function should error at the variable analysis stage, however, NiLang is playing lazy to allow it pass. Wish to hear your advices about how to make the second function error correctly. I have a naive solution that records the input arguments and allocated variables. Is it possible to also detect global variables?