--- | this just re-throws any exceptions received. The point of this
--- is that if -fbreak-on-excepsions is on, we only get a chance to break
--- for synchronous exceptions, and this turns an async exception into
--- a sync exception, so for instance a ^C exception will break right here
--- unless it is caught elsewhere.
+-- We want to turn ^C into a break when -fbreak-on-exception is on,
+-- but it's an async exception and we only break for sync exceptions.
+-- Idea: if we catch and re-throw it, then the re-throw will trigger
+-- a break. Great - but we don't want to re-throw all exceptions, because
+-- then we'll get a double break for ordinary sync exceptions (you'd have
+-- to :continue twice, which looks strange). So if the exception is
+-- not "Interrupted", we unset the exception flag before throwing.
+--