Prevent overriding an array

[Rudi79]

@Sleepy

function next_step(x, i)
    x[i] = x[i]+1
    return x
end

x = [0,0,0,0]
x_a = next_step(x, 1)

Try

function next_step(x, i)
    y = copy(x)
    y[i] = y[i]+1
    return y
end

I would strongly suggest having a look into the manual.