Re: [TCLCORE] Prototype Implementation of TIP 672 - $(expr) Syntax

[da S. P. J <pet...@fl...>]

I recall that on one occasion when I suggested this kind of syntax I was told there was working code that used $(...) as an array index for an array whose name was the null string.

From: EricT <tw...@gm...>
Date: Friday, October 17, 2025 at 16:23
To: tcl...@li... <tcl...@li...>
Cc: et...@ro... <et...@ro...>
Subject: [TCLCORE] Prototype Implementation of TIP 672 - $(expr) Syntax
Hello Tcl Core Team, I have developed a working prototype implementation of TIP 672, which adds the $(expression) syntax as a more intuitive alternative to [expr {expression}]. Repository: https: //github. com/rocketship88/tcl-tip-672-prototype

Hello Tcl Core Team,

I have developed a working prototype implementation of TIP 672, which adds the $(expression) syntax as a more intuitive alternative to [expr {expression}].

Repository: https://github.com/rocketship88/tcl-tip-672-prototype<https://urldefense.us/v2/url?u=https-3A__github.com_rocketship88_tcl-2Dtip-2D672-2Dprototype&d=DwMFaQ&c=MASr1KIcYm9UGIT-jfIzwQg1YBeAkaJoBtxV_4o83uQ&r=BRyGRggIJd8TmKOhvEmGElFuDuCl3O5mT8opva3f-Uc&m=lqqkjbudEIhZyWU1Mr-DT_aw0n-0q0fJeE2A7RRQpS2HwF0EA62yINzmRaXGPetk&s=S65xARxittuq7tg4WiuXdT0ervfhA8RXzsEv3-NxhGA&e=>

The implementation is minimal, modifying only two files (tclParse.c and tclNamesp.c) with approximately 100 lines of changes. The key modification converts the existing two-way branch in Tcl_ParseVarName to a three-way branch, with the new path handling $(...) by creating a synthetic [expr {...}] command string.

Key Accomplishments:

Full bytecode compilation: The synthetic string approach integrates seamlessly with the existing compiler, producing identical optimized bytecode as [expr {...}]. The disassembler output (shown in the README) demonstrates efficient variable loading with no runtime parsing overhead.

Proven approach: Jim Tcl has used this syntax successfully for years

Comprehensive testing: Works correctly with string interpolation, variable scoping, error handling, and interactive mode

Known Limitations:

Memory leak: The synthetic string is allocated but not tracked for cleanup in Tcl_FreeParse. This requires core team guidance on the preferred solution (modify Tcl_Parse structure vs. thread-local tracking).

Error messages: Currently show the synthetic command rather than the original $(...) syntax, though this is arguably helpful for debugging.

Questions for the Team:

What is the preferred approach for tracking synthetic strings for cleanup?
Is this prototype architecture acceptable for Tcl 9.x?
Are there concerns with the synthetic string approach that I should address?

The complete implementation with side-by-side diffs is available in the repository. I'm happy to refine the code based on your feedback and would appreciate any guidance on moving this forward.

Best regards,
Eric