Arbitrary call order in Julia

gistfile1.jl

function join_function(a, b :: Union(String, Char))
    # Julia's is a bit too permissive on types
    join(a, b)
end

list = [1, 2, 3]
separator = ", "
macro call(symbol_a, symbol_b, symbol_c)
    a, b, c = eval(:( $symbol_a, $symbol_b, $symbol_c))

    if isa(a, Function)
        if method_exists(a, (typeof(b), typeof(c)))
            return a(b, c)
        else
            return a(c, b)
        end
    elseif isa(b, Function)
        if method_exists(b, (typeof(a), typeof(c)))
            return b(a, c)
        else
            return b(c, a)
        end
    else  # c is the function
        if method_exists(c, (typeof(a), typeof(b)))
            return c(a, b)
        else
            return c(b, a)
        end
    end
end

println(@call join_function list separator)
println(@call join_function separator list)
println(@call separator join_function list)
println(@call separator list join_function)
println(@call list join_function separator)
println(@call list separator join_function)