Adding keyword parameters to Tcl procs
The article introduces a custom `proc*` command in Tcl to implement keyword parameters, addressing limitations in standard commands and discussing the use of quasiquoting and challenges in metaprogramming.
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The article discusses the addition of keyword parameters to Tcl procedures, addressing a common frustration among programmers regarding the lack of named and order-agnostic parameters in some programming languages. The author highlights that while Tcl has UNIX-like options in its standard commands, these features are not available in the `proc` or `apply` commands. The article presents a custom implementation of a `proc*` command that allows for keyword parameters, demonstrating its functionality with examples. The author also explains the underlying mechanics of this implementation, including the use of quasiquoting for code generation, which is necessary due to Tcl's limitations in metaprogramming. The article concludes with a reflection on the challenges of using regular expressions for metaprogramming in Tcl, emphasizing the complexity involved in creating a flexible and functional system for handling keyword parameters.
- Tcl lacks built-in support for keyword parameters in its standard commands.
- The author introduces a custom `proc*` command to implement keyword parameters.
- The implementation includes examples demonstrating the functionality of keyword parameters.
- Quasiquoting is used for code generation due to Tcl's metaprogramming limitations.
- The article reflects on the challenges of using regular expressions for metaprogramming in Tcl.
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5 commentsMy own nxproc extension is more comprehensive. (See wiki [0].)
The extension enables named arguments, regular positional arguments, and 'rest' arguments, nxargs and nxunknown. Nxproc also provides (optional) type-checking of procedure arguments. (Types: string, number, bool and enumerated. Enums are lists of values restricting what the arg can contain.)
Nxproc supports TclOO with nxcontructor and nxmethod commands -- same feature set as "plain" nxproc. Also provides case-insensitive '-ci' variants, and runtime display of named-argument default/actual values and types.
Nxproc is a Tcl C extension. Bundle has Windows, Linux binaries. Compiles easily on other platforms.
I think it would be very useful to turn ad_proc into a built-in command and incorporate it into TCL.
I also had further fun with wrapping "proc" by implementing a "pyproc" which called out to Python while looking like a normal Tcl proc.
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