On 12/05/2012 05:38 AM, John P. Rouillard wrote:
>
> Hi Risto and all:
>
> I have been looking at the 2.7 alpha release and I have a few
> comments. The functions that deal with setting a variables from some
> context seem to have different calling conventions
>
> copy, empty, pop, shift
>
> all take "<name> %<var>" as arguments while:
>
> exists, getsize, getaliases, getltime, getctime
>
> take "%<var> <name>". Is there a reason for this discrepency? I can
> see getting really confused about which goes where depending on the
> function. I would suggest making all of them consistant and use
> "<name> %<var>" for all the functions above.
One of the reasons was that there are already getwpos and setwpos
actions which record/set the operation window position into/from its
first variable operand:
getwpos %<var> <offset> [<string>]
setwpos <time> <offset> [<string>]
getctime and setctime do exactly the same things for the context, so it
seemed a better idea to have the same operand ordering.
When you look at copy, empty, pop, shift, these actions work on event
data stored to contexts, while exists, getsize, getaliases, getltime,
getctime are about getting or setting metadata information for contexts.
Initially, I was actually using a reverse ordering in one intermediate
release, but become fairly confused by it :(
Finally, it looked a better idea to me to have all actions which query
or set metadata have the same layout.
>
> Functions like assign, eval, call or lcall sensibly have the variable
> as the first argument since the second argument is potentially
> multiple words long (a string and perl code, param lists etc).
>
> Also to make while/if more useful I think a shortcut like:
>
> if exists(<name>) ( action_list ) else ( action_list2 )
>
> while exists(<name>) ( action_list )
>
> is more readable compared to:
>
> exists<name> %B; if %B ( action_list ) else ( action_list2 )
>
> exists<name> %B; while %B ( action_list; exists<name> %B )
>
> In general maybe any function that sets a variable can return that
> value for an if or while condition clause. So 'exists' can be replaced
> by 'getsize', 'getaliases', 'pop', 'getltime' ....
To clarify a bit why only action list variables are allowed for 'if' and
'while' -- initially I was thinking of allowing any constructs which
would go through substitution or other intepretation, but this would
again add run time complexity. Depending on the type of an argument, you
would have to do a number of if-elsif's inside perl code, which slows
down the code. Moreover, doing variable substitutions is always an
expensive process.
While things above would be somehow manageable for 'if', imagine now the
case for 'while' action. For example, the substitutions would have to be
carried out repeatedly, but since substituted values could contain
substrings which look like match variables, they would have to be masked
separately, before actual substitution, etc.
In contrast, action list variables are implemented as a hash table, so
verifying if an action list variable evaluates true is as simple as:
exists($hash{$var}) && $hash{$var}
These checks are fast and efficient even if the while loop gets executed
many times. Moreover, there is no need to deal with logical
contradictions at which point which thing should be masked or substituted.
So the current approach is mainly motivated by simplicity of design and
efficient execution.
with kind regards,
risto
>
> --
> -- rouilj
> John Rouillard
> ===========================================================================
> My employers don't acknowledge my existence much less my opinions.
>
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