A loop variable read before its within-loop redefinition gets a maybe marker to that def (e.g. x_2 may read the prior iteration's x_1 in for(...) { x_1 <- x_2 + 1 }); with environment, this uses all defs live at loop exit.
x_2
x_1
for(...) { x_1 <- x_2 + 1 }
environment
Optional
A loop variable read before its within-loop redefinition gets a maybe marker to that def (e.g.
x_2may read the prior iteration'sx_1infor(...) { x_1 <- x_2 + 1 }); withenvironment, this uses all defs live at loop exit.