Re: Function Calls by Address

[Robert Dewar <robert_dewar@my-deja.com>]

In article <ar3rq7.7qb.ln@ds9.klebsch.de>,
  mario@klebsch.de (Mario Klebsch) wrote:
> ANd there are a lot of nice things, you only can to that
elegant with
> nested procedures. Nested procedures have full access to all
local
> variables of the enclosing procedures. If you want to do it in
C, you
> have to use static variables and will loose reentrancy.


Right Mario, this is a VERY important point. It is often
the reason for C library routines being non-thread safe.
Unfortunately the fix in these C library routines is
often to add locks to protect these unnecessary global
variables.

As an example, suppose you are writing printf. Well you
certainly do not want to write this as one giant function,
so you write it as multiple functions. Now you *should*
pass around all global variables, such as the buffer into
which characters are being written, but it is awfully tempting
to make this a global variable, with the result that you lose
thread safety. In Ada, you would write printf with nested
subprograms that accessed the buffer pointer as a non-local
uplevel reference (but the variable would be local to printf
itself).

With regard to name space pollution, it is more than just this.
The point is that if you see a nested procedure, you know
immediately that you only have to understand it in the context
of its enclosing procedure, and indeed if you can ignore this
code in the reading you are doing right now, you can immediately
and easily ignore all the nested procedures, knowing that you
have not missed anything.


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