Reject the current parse. This causes the compiler to reject the interpretation of the program text that resulted in execution of the code that invoked this method. The argument is a description of the parse rejection, but in positive terms that primarily assert what the caller was expecting (on the compiler's behalf). It is, of course, also useful to state what was actually discovered.

Note that the Avail compiler attempts, in parallel, many different parses of a statement. If the only parses syntactically accepted by the compiler are semantically rejected by callers of this method, then and only then is the statement deemed invalid and the arguments of such calls emitted by the compiler as error messages to assist the programmer in correcting the rejected statement.

This method may only be invoked from the body of a macro function or a semantic restriction function: it should only be invoked by the Avail compiler, never by a semantically valid Avail program.