[Python-Dev] Terminology for PEP 343 (original) (raw)

Michael Walter michael.walter at gmail.com
Mon Jul 4 06:50:32 CEST 2005

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, " "xml.Tags used to wrap a block will print '' before the block is entered, and '' 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 ." > > > > Doesn't "guard" suggestion conditional execution? > > > > > > Raymond > >

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