Translates all return statements into an invocation of the next iteration. This can be either - "continue LOOP_LABEL": Outside closures - "throw LOOP_EXCEPTION": Inside closures Moreover, before adding the recur statement the iteration parameters (originally the method args) are set to their new value. To prevent variable aliasing parameters will be copied into temp vars before they are changes so that their current iteration value can be used when setting other params. There's probably place for optimizing the amount of variable copying being done, e.g. parameters that are only handed through must not be copied at all.