During execution of a procedure, if a condition statement is reached and the defined condition, x is not met, then execution of the entire procedure is restarted.

A condition statement can be added as a top-level line inside any procedure.  By "top-level" we mean that it cannot occur inside of any compound statement like a loop or if statement.

p := proc() local a := rand(-1..1)(); condition: a <> 0; a; end:

$\left\{\mathrm{seq}\left(p\left(\right)\&comma;i=1..20\right)\right\}$

$\left\{\mathrm{-1}\&comma;1\right\}$

The condition command was introduced in Maple 18.

For more information on Maple 18 changes, see Updates in Maple 18.