Glenn JackmanDon PorterGlenn Jackman$Revision: 1.6 $

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.

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: ICAgICAgIHByb2MgdGVzdCB7b25lIHt0d28gMn0ge3RocmVlIHszIDQgNX19IGFyZ3N9IHtyZXR1cm59 We want to determine the formal arguments for this procedure. We want some method to return the list: ICAgICAgIG9uZSB7dHdvIDJ9IHt0aHJlZSB7MyA0IDV9fSBhcmdz [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: ICAgICAgIHByb2MgaW5mb19hcmdzX3dpdGhfZGVmYXVsdHMge3Byb2NuYW1lfSB7ICAgICAgICAgICBzZXQgYXJnc3BlYyBbbGlzdF0=ICAgICAgICAgICAjIFtpbmZvIGFyZ3NdIHRocm93cyBhbiBlcnJvciBpZiAkcHJvY25hbWUgaXMgbm90IGEgcHJvY2VkdXJlLg==ICAgICAgICAgICBmb3JlYWNoIGFyZyBbaW5mbyBhcmdzICRwcm9jbmFtZV0gew==ICAgICAgICAgICAgICAgaWYge1tpbmZvIGRlZmF1bHQgJHByb2NuYW1lICRhcmcgdmFsdWVdfSB7ICAgICAgICAgICAgICAgICAgIGxhcHBlbmQgYXJnc3BlYyBbbGlzdCAkYXJnICR2YWx1ZV0=ICAgICAgICAgICAgICAgfSBlbHNlIHs=ICAgICAgICAgICAgICAgICAgIGxhcHBlbmQgYXJnc3BlYyAkYXJnICAgICAgICAgICAgICAgfQ==ICAgICAgICAgICB9ICAgICAgICAgICByZXR1cm4gJGFyZ3NwZWM=ICAgICAgIH0=ICAgICAgIGluZm9fYXJnc193aXRoX2RlZmF1bHRzIHRlc3QgIDsjID09PiByZXR1cm5zIHtvbmUge3R3byAyfSB7dGhyZWUgezMgNCA1fX0gYXJnc30= A more sophisticated scripted solution is to overload the [info] command itself, as described in the Wiki at 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 newsgroup in the thread

Add [info formalargs] to the set of subcommands for Tcl's built-in [info] command, with syntax: IGluZm8gZm9ybWFsYXJncyAkcHJvY05hbWU= 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.

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: These all collide with the "arg", "ar", "a" shorthands for [info args procname]. And args_with_defaults is just *way* too ugly.Either of these could be used. This collides with the "f" shorthand for [info functions]This collides with the "pa" shorthand for [info patchlevel]This collides with the "pro" and "pr" shorthands for [info procs ?pattern?]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].

Refer to the submitted patch, which implements an subcommand named [info fullargs], at:

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 as another approach to letting people extend Tcl built-in commands with their own custom subcommands.

This document has been placed in the public domain.