[Python-Dev] Terminology for PEP 343

[Michael Walter]

Oh, I remember. Agreed, it is most probably a bad choice then.

One part of my brain likes:

  "By wrapping a block in/with[*] a decimal.Context, <elaborate on
consequences>"
  "xml.Tags used to wrap a block will print '<tag>' before the block
is entered, and '</tag>' after execution has left."

What do you think?

[*] I'm not sure what's the correct English version, sorry.. if it is
"with", it migh be a nice way to place a hyperlink to the language
reference.


On 7/3/05, Raymond Hettinger <python at rcn.com> wrote:
> I'm referring to the specific meaning of "guard" in a computer science
> context:
> 
>      http://www.computer-dictionary-online.org/guard.htm?q=guard
> 
> From David Gries, The Science of Programming, if statement contains two
> entities of the form B --> S wehere B is a Boolean expression and S a
> command.  B --> S is called a guarded command.
> 
> I believe that terminology is rooted in Dijkstra's language of guarded
> commands (used to express and facilitate program proofs).  They are
> essentially the same as conditionally executed statements but may be
> executed non-deterministically:
> 
>     http://cs-exhibitions.uni-klu.ac.at/contentGuardedCommand.php
> 
> Also, I believe the pattern matching part of Prolog clauses are called
> guards; however, the conditional execution is deterministic (the first
> match is the one that fires) and potentially recursive.
> 
> This terminology is used consistently among various functional
> programming languages.  From,
> http://www.cs.ecu.edu/~karl/astarte/glossary.html , "A guard in a case
> is the condition that is being tested. For example, in case a => b,
> expression a is the guard."
> 
> In predicate calculus, the phrase, "strengthening the guard" has a
> specific meaning with the "guard" part being consistent with the above.
> One example:
> 
>    http://www.cs.utexas.edu/users/psp/unity/notes/07-89.pdf
> 
> IOW, guard is a specific term, not an amorphous metaphor that can be
> accurately applied to the enter/exit or enter/leave pair.
> 
> 
> Raymond
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: Michael Walter [mailto:michael.walter at gmail.com]
> > Sent: Sunday, July 03, 2005 10:28 PM
> > To: Raymond Hettinger
> > Cc: rrr at ronadam.com; python-dev at python.org
> > Subject: Re: [Python-Dev] Terminology for PEP 343
> >
> > Hmm, I think I'm seeing mostly the (guarded) entry/exit part of
> > "guard" metaphor, but I see what you mean (not allowing "entry", so to
> > say, right?). Not sure.
> >
> > Michael
> >
> > On 7/3/05, Raymond Hettinger <python at rcn.com> wrote:
> > > >   "Guarding a scope with a decimal.Context() object <explain
> effect>."
> > >
> > > Doesn't "guard" suggestion conditional execution?
> > >
> > >
> > > Raymond
> > >
>