Parsing UPF - Embedding TCL interpreter with python

This post is about quirky idea to parse UPF for fun and profit. I started with writing Lark BNF, To a man with a hammer, everything looks like a nail :) But gave up on the idea as i will end up writing frontend for TCL. So, I was mentally blocked for some time.

Then it hit me, I can use full-blown TCL interpreter to parse the actual UPF and pass it back to python for processing. The problem how to do it?

Apparently, TCL can accept user-defined handler for commands called _unknown. The idea is getting the command name and arg and create a json and send it back to python socket (not show in the snippet yet.)

# Globals passed to python
set command_name "TMP"
set command_args ""

# Handle unsupport commands
rename unknown _unknown;
proc unknown {args} {
    # puts stderr "Unknown Command: $args"
    # puts [llength $args]
    global command_name
    global command_args

    set command_name [lindex [info level 0] 0]
    
    set result ""
    foreach x $args {
        append result $x
    }
    set command_args $result
}

The easiest way to run TCL from python is using tkinter.Tcl. The first command is calling the common error handler and then parsing TCL(UPF) and passing it to the tclsh

import tkinter
    
  tclsh = tkinter.Tcl()

    tclsh.eval("source {tcl/upf_commands.tcl}")

    f = open(args.filename,"r")
    lines = f.readlines()
    lines = "".join(lines)
    tclsh.eval(lines)

The next step is complete the interface from TCL to python to call python stuff for each UPF command.