Either in the start or end of a loop block, evaluates a Boolean expression and, if it results true, allows the (re-)execution of the block instructions
Implemented by: ansifull, cbmv7, cbmv3.5, ataplus, atxl, GWBASIC, bwbasic, bw32, ABasiC, QBasic, VBDOS, FreeBASIC, Gambas, ugBASIC, EndBASIC
With variations: decbasic
Also written as: