An equivalent idea to that suggested in E12.33 is already to be found in C-like languages in the break or continue statements that they allow within their various structured statements like switch, do, for and while. How would you extend the grammar and parser for Parva to incorporate these statements subject to the same sort of constraints?

E12.33

The simplest applications of the loops we have considered so far are structured – they have only one entry point, and only one exit point. Some languages allow a slightly less structured loop, which has only one entry point, but which allows exit from various places within the loop body. An example of this might be as follows.

The syntax for these new statements appears to be trivial

but this is deceptively ingenuous. Loop Statements can be nested, and Exit Statements may only appear within the body of a Loop Statement. Can you find context-free productions that will allow you to incorporate these statements into Parva? If not, can you impose the necessary constraints in some other way?