TIP: 65 Title: Enhanced [info args] Version: $Revision: 1.6 $ Author: Glenn Jackman Author: Don Porter Author: Glenn Jackman State: Rejected Type: Project Vote: Done Created: 18-Sep-2001 Post-History: Tcl-Version: 8.5 ~ Abstract This TIP proposes a new subcommand to the [[info]] command be added that would return the list of arguments, together with any default values in the same format as the ''args'' parameter to the [[proc]] command. ~ Introduction The [[proc]] man page defines ''args'' as: > ... the formal arguments to the procedure. It consists of a list, possibly empty, each of whose elements specifies one argument. Each argument specifier is also a list with either one or two fields. If there is only a single field in the specifier then it is the name of the argument; if there are two fields, then the first is the argument name and the second is its default value. Suppose we define a procedure like this: | proc test {one {two 2} {three {3 4 5}} args} {return} We want to determine the formal arguments for this procedure. We want some method to return the list: | one {two 2} {three {3 4 5}} args [[info args]] fails us because it does not return default values, only the list of argument names {one two three args}. The [[info default]] command exists, and does partially what we want. However [[info default]] only operates on a single argument. To determine the complete list of arguments with default values, we must iterate over the arguments returned by [[info args]]. We would define a procedure like: | proc info_args_with_defaults {procname} { | set argspec [list] | # [info args] throws an error if $procname is not a procedure. | foreach arg [info args $procname] { | if {[info default $procname $arg value]} { | lappend argspec [list $arg $value] | } else { | lappend argspec $arg | } | } | return $argspec | } | info_args_with_defaults test ;# ==> returns {one {two 2} {three {3 4 5}} args} A more sophisticated scripted solution is to overload the [[info]] command itself, as described in the Wiki at http://wiki.tcl.tk/wrappingCommands It would be much more convenient to be able to rely on the [[info]] command itself to return the desired information, particularly since it ''almost'' does what we want already. ''This topic was originally raised in the news:comp.lang.tcl newsgroup in the thread http://groups.google.com/groups?th=4b0d5dba85d2c160'' ~ Specification Add [[info formalargs]] to the set of subcommands for Tcl's built-in [[info]] command, with syntax: | info formalargs $procName This command will raise an error if ''$procName'' is not the name of a proc. Otherwise, it will return a list of formal arguments of the named proc, along with their default values, if any, in a format suitable for passing to the [[proc]] command as a second argument. ~ Rationale With the goal of maintaining backwards compatibility in mind, two possibilities arise: adding a new switch to the existing [[info args]] command, and adding a completely new subcommand to [[info]]. Adding a switch to [[info args]] may break backwards compatibility. If we use the syntax [[info args ''?-withdefaults? procname'']], there may be trouble with existing scripts containing a procedure named "-withdefaults". The syntax [[info args ''procname ?-withdefaults?'']] is completely backwards compatible. However, among Tcl commands that take subcommands, there is currently some inconsistency as to where switches should appear. [[clock]] subcommands place these options after required parameters. [[namespace]] and [[package]] subcommands place these options before required parameters. Some [[file]] subcommands put them before, some after. Currently, no [[info]] subcommands take switches. Rather than compound to this inconsistency, creating a new [[info]] subcommand feels cleaner. Possible names include: argspec, arglist, args_with_defaults: These all collide with the "arg", "ar", "a" shorthands for [[info args ''procname'']]. And ''args_with_defaults'' is just *way* too ugly. formalargs, fullargs: Either of these could be used. This collides with the "f" shorthand for [[info functions]] parameters: This collides with the "pa" shorthand for [[info patchlevel]] prototype: This collides with the "pro" and "pr" shorthands for [[info procs ''?pattern?'']] signature: This could be used, as it does not collide with any shorthand for either [[info script]] or [[info sharedlibextension]]. The term "signature" has meaning in the Java and C++ worlds: the function name and its arguments together comprise the signature. The purpose of this TIP is to return only the arguments with any defaults, so to avoid any potential confusion I will rule out "signature". Of the remaining possibilities, my choice would be "formalargs". The term "formal arguments" is used in the [[proc]] man page. "formalargs" also incorporates the word "args", indicating a relationship to [[info args]]. ~ Reference Implementation Refer to the submitted patch, which implements an subcommand named [[info fullargs]], at: http://sourceforge.net/tracker/index.php?func=detail&aid=461635&group_id=10894&atid=310894 ~ Reasons for Rejection Those voting against this proposal believed that since the desired functionality is already possible with a short script of just a few Tcl commands, it would be unnecessary bloat to add another subcommand. Some also pointed to [112] as another approach to letting people extend Tcl built-in commands with their own custom subcommands. ~ Copyright This document has been placed in the public domain.