# This file is a part of Julia. License is MIT: http://julialang.org/license

export @var

immutable Binding
    mod::Module
    var::Symbol
    defined::Bool

    function Binding(m, v)
        if !isdefined(m, v)
            new(m, v, false)
        else
            new(Base.binding_module(m, v), v, true)
        end
    end
end

function splitexpr(x::Expr)
    isexpr(x, :macrocall) ? splitexpr(x.args[1]) :
    isexpr(x, :.)         ? (esc(x.args[1]), x.args[2]) :
    error("Invalid @var syntax `$x`.")
end
splitexpr(s::Symbol) = :(current_module()), quot(s)
splitexpr(other)     = error("Invalid @var syntax `$other`.")

isvar(x) = isexpr(x, [:macrocall, :.])
isvar(::Symbol) = true

macro var(x)
    :(Binding($(splitexpr(x)...)))
end

Base.show(io::IO, x::Binding) = print(io, "$(x.mod).$(x.var)")