[Asterisk-Users] Re: Bison, Flex, Conditional Expression

[Steve Murphy]

To any that may be interested in the implementation of the conditional expression
in the expression parser (ast_expr2*) in asterisk, I've filed the patch at:

http://bugs.digium.com/view.php?id=4459

Right now, a comment has been added noting that the IF func provides this capability,
and asks if both would really be necessary. It's a good question. I haven't been 
following the addition of this new set of capabilities in asterisk, but see that
"show functions" returns:

DB                    DB(<family>/<key>)                   Read or Write from/to the Asterisk database
ENV                   ENV(<envname>)                       Gets or sets the environment variable specified
IF                    IF(<expr>?<true>:<false>)            Conditional: Returns the data following '?' if true else the data following ':'
EXISTS                EXISTS(<data>)                       Existence Test: Returns 1 if exists, 0 otherwise
ISNULL                ISNULL(<data>)                       NULL Test: Returns 1 if NULL or 0 otherwise
CDR                   CDR(<name>[|options])                Gets or sets a CDR variable
STRFTIME              STRFTIME([<epoch>][,[timezone][,for  Returns the current date/time in a specified format.
LEN                   LEN(<string>)                        Returns the length of the argument given
REGEX                 REGEX("<regular expression>" <data>  Regular Expression: Returns 1 if data matches regular expression.
FIELDQTY              FIELDQTY(<varname>,<delim>)          Count the fields, with an arbitrary delimiter
GROUP_LIST            GROUP_LIST()                         Gets a list of the groups set on a channel.
GROUP                 GROUP([category])                    Gets or sets the channel group.
GROUP_MATCH_COUNT     GROUP_MATCH_COUNT(groupmatch[@categ  Counts the number of channels in the groups matching the specified pattern
GROUP_COUNT           GROUP_COUNT([groupname][@category])  Counts the number of channels in the specified group
CHECK_MD5             CHECK_MD5(<digest>,<data>)           Checks an MD5 digest
MD5                   MD5(<data>)                          Computes an MD5 digest
IAXPEER               IAXPEER(<peername>[:item])           Gets IAX peer information
SIP_HEADER            SIP_HEADER(<name>)                   Gets or sets the specified SIP header


How are these functions used? The last sentence of the README.variables file says:


Certain functional variables may be accessed with $(foo <args>).  A list
of these functional variables may be found by typing "show functions"
at the Asterisk CLI.

So, I guess you could say:

SetVAR(var=$(IF a=b?true:false))

or do I have to say:

SetVAR(var=$(IF $[a=b]?true:false))
or
SetVAR(var=$(IF $[a=b]?$[possibly_more_complicated_true_expr]:$[possibly_more_complicated_false_expr]))

[ between the two sets above, the second "feels" more realistic than the first, as the actual
evaluation of a=b most likely will have be done by the expression parser... if not, the expression
parser will no longer be necessary]

vs:

SetVAR(var=$[a=b ? true :: false])

As I said, I haven't been following the Function additions at all (yet), and haven't
actually tried to fit any of them in my extensions.conf (yet).

Someone who's more involved with this might show some examples of how functions are
used, and maybe we can see then which method might be best, if any, and whether it might be
better to toss one, or keep them both...

Can anyone help cast some more light on how Functions like IF would be used in extensions.conf?
Was I right about the usage above?

murf