Yeah, you're right. Allowing both is a non-starter. Well, it could try to infer the direction by looking which way the bindings go, e.g. [a for b in c for a in

Yeah, you're right. Allowing both is a non-starter. Well, it could try to infer the direction by looking which way the bindings go, e.g. [a for b in c for a in b] would represent foreach(c, foreach(b)) because otherwise b would be unbound in the outer loop... but that doesn't sound like an especially good idea, having syntax change depending on which variable bindings exist. So all in all, I guess I'd prefer it to always go right-to-left: [a for a in b for b in c]. That would be consistent with nested comprehensions (which read right-to-left), but not with nested loops (which read top-to-bottom). YMMV.