3.7.11 A Pure (Reentrant) Parser

[slipbits]

The first sentence reads "A /reentrant/ program is one which does not 
alter in the course of execution; in other words, it consists entirely 
of /pure/ (read-only) code. "

Some points which confuse me:

1. "alters" what? The object is not mentioned. Did you mean that it
   does not alter non-local data and input parameters? See paragraph 2
   "The standard Yacc interfaces are inherently nonreentrant, because
   they use statically allocated variables" which alludes to modifying
   non-local data.
2. "...it consists entirely of /pure/ (read-only) code. " This is
   confusing to me. In modern machines, code is read-only (this wasn't
   the case in computers from the 50's, 60's, and I believe 70's in
   which it was possible to alter the executing code. Did you mean that
   the code did not alter non-local data and parameters? If it doesn't
   alter anything then the function does nothing.
3. I'm not sure but I believe the standard definition of reentrancy is
   that the external environment is unaltered. This is tantamount to
   not altering data, objects, external objects, etc., that is, status
   quo ante. After the execution of the code changes to the environment
   external to the code is non-detectable. However, returning values
   (of functions) and returning data through alteration of the input
   parameters (either [inout] or [out]) is perfectly fine.

This section may be in error.

thanks
art