Re: Records
Re: Records
- Subject: Re: Records
- From: Christopher Nebel <email@hidden>
- Date: Thu, 3 Nov 2005 16:56:24 -0800
On Nov 3, 2005, at 3:02 PM, Mark J. Reed wrote:
On 11/3/05, Christopher Nebel <email@hidden> wrote:
The short version is that if the identifier consists entirely of
lowercase letters, numbers, and underscores, *and* it doesn't
match any application- or AppleScript-defined terminology (such as
"file"), then the bars will be discarded. Long version, including
why it works that way, available on request, but it's not really
useful.
Never let it be said that I let a little thing like lack of utility
get in the way of knowledge acquisition! :) I would be quite
interested in the long version.
It seems like discarding the pipes runs the risk of the semantics
of a script changing if it's decompiled and recompiled in an
environment different from that in which it was originally written...
You might think so, but it doesn't. Well, it could, but only if you
really worked at it. Here's the deal:
AppleScript variables (actually, identifiers in general) are case-
insensitive: "this" is the same variable as "This" or "ThiS". When
compiling, variable names are "canonified" by transforming all
letters to lowercase -- this canonified name is then the key used to
reference the variable, and the original name is stashed off to the
side. What the vertical bars do is to (1) inform the parser that
every character until the closing bar is part of a single identifier,
so you can include spaces, punctuation, kanji, or what have you, but
more importantly for this discussion, (2) they suppress the
canonification step -- the key is the identifier exactly as you wrote
it.
When it's time to decompile, AppleScript compares the key (the
canonified name) to a re-canonification of the original name, also
taking defined terminology into account. If they match, then it
prints the original name. If they don't match, which is only
possible if you originally wrote it using bars or if some new
terminology showed up such as by adding a scripting addition, then it
puts bars around the name. It doesn't actually remember whether you
wrote it with bars or not; it effectively derives that information.
However, if you |bar| a name that already matches the canonified
form, then it winds up discarding the bars.
Getting back to the question of changing semantics, it generally
works, and it works better than remembering whether or not bars were
used at compile time, because decompilation uses the environment as
it exists at decompilation time. You could manage to trick it by
compiling a script, changing the environment, decompiling it (some
identifier is assumed to lose its bars at this point), changing the
environment back, and then recompiling the raw text from step 3.
However, raw text scripts are already not guaranteed to be portable
across environment changes, so that's not really an issue.
--Chris Nebel
AppleScript and Automator Engineering
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| References: | |
| | >Re: Records (From: Christopher Nebel <email@hidden>) |
| | >Re: Records (From: "Mark J. Reed" <email@hidden>) |