If the slash is big enough to open up, probably not repairable. You'll have to bite the bullet and pay up for another tyre I think.
While you might be able to limp along with a repaired tyre, if you run it at any real pressure, there's always the risk of the split opening up. If that happens, the tyre could deflate instantaneously. Not a fun scenario if you're dealing with traffic at the time.
Better luck with the next tyre. And watch out for that broken glass.