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I've written a small Tcl/Tk script for a friend that displays the current time, as well as a quote. He uses it in some project with a Raspberry Pi, and since I didn't want to cobble up something up in Qt, PyQt, or some kind of website, I tried to write something in Tcl/Tk.

Demo

Here is how it looks in the end:

screenshot of program

Requirements

This script assumes that you have fortune available an in your $PATH.

Script

#!/usr/bin/env tclsh

proc every {ms body} {
    eval $body
    after $ms [info level 0]
}

label .time -bg black -fg white -font {Arial 150} -textvar ::time -pady 30
every 1000 { set ::time [clock format [clock sec] -format "%T"] }

label .fortune -bg black -fg white -font {Arial 15}  -textvar ::fortune
every 30000 { set ::fortune [exec fortune -s] }

pack .time -fill both
pack .fortune -fill both -expand 1

. configure -bg black

wm attributes . -fullscreen 1

bind . <q> exit

What to review

This is my first script in Tcl/Tk. Feel free to commend on anything, especially if there's some kind of common style I'm missing.

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1 Answer 1

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Nice code. I only see a couple of items

  1. add package require Tk to be explicit you need tk
  2. use uplevel #0 $body instead of eval
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  • \$\begingroup\$ Ad 1) I had that in the original Raspberry code and another rewrite, completely missed it in my last one. ad 2) can you explain the difference between uplevel #0 $body and eval? \$\endgroup\$
    – Zeta
    Commented Feb 1, 2018 at 20:09
  • \$\begingroup\$ uplevel evaluates the given code in a particular "stack frame". This is important as each frame the current execution stack will have a different set of (local) variables. The level #0 is the zero-th level from the bottom of the stack, in other words the global frame. In your programming, you are explicitly setting global variables, so eval and uplevel #0 have identical effects. \$\endgroup\$
    – glenn jackman
    Commented Feb 1, 2018 at 21:35
  • \$\begingroup\$ where uplevel is really handy is in writing custom loops like myforeach foo $list {some body here} where you need to evaluate the loop body 1 level up in the stack frame (where the myforeach command invocation resides) \$\endgroup\$
    – glenn jackman
    Commented Feb 1, 2018 at 21:41
  • \$\begingroup\$ Is there some kind of style guide? Or does "usual" Tcl code look like mine? \$\endgroup\$
    – Zeta
    Commented Feb 6, 2018 at 6:46

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