Introduction to Tcl and Tk

1
Introduction to Tcl and Tk

• Outline
• The Tcl Language
• The Tk Toolkit
• Tk Applications
• Composing Applications
• Status and Conclusions
• Goal
• Understand basics of Tcl and Tk
• Understand Tk/Tcl philosophy
• Reading
• Ch. 5-9, Practical Programming in Tcl and Tk

2
Overview

• What
• Tcl embeddable scripting language
• Tk X11/Windows/Mac toolkit and widgets based on
  Tcl
• Principle
• single interpretive language controls all aspects
  of all interactive applications
• function
• interface
• composition of pieces
• communication between applications
• Results
• higher- level graphics programming - simpler, 10X
  faster
• greater power - more programmable, programs work
  together

3
Tcl Tool Command Language

• Problem
• interactive programs need command languages
• traditionally redone for each application
• result weak, quirky
• Emacs and csh nice, but cannot reuse
• Solution Tcl
• command language embeddable C library
• powerful features procedures, variables, lists,
  expressions, loops, etc.
• extensible by applications

4
Language Philosophy

• Language classes
• large application implementation (structure,
  performance important)
• scripting, extensions
• interactive commands (structure bad, performance
  not critical)
• One language cant meet all three needs?
• Tcl goals
• simple syntax (for humans)
• programmable
• easy to interpret
• simple interface to C/C procedures

C
Tcl
5
Tcl Syntax

• Basic syntax like shells
• words separated by spaces
• cmd arg arg arg . . .
• commands separated by newlines, semicolons
• commands return string results
• Simple substitution rules
• variables
• set a b
• command results
• set a expr b2
• complex arguments
• if alt0
• puts stdout a is negative

6
More on the Tcl Language

• Rich set of built-in commands
• variables, associative arrays, lists
• arithmetic expressions
• conditionals, looping
• procedures
• access to files, system commands
• Only data type is string
• easy access from C/C
• programs and data are interchangeable

7
Example Factorial

• proc fac x
• if xlt1
• return 1
• expr xfac expr x-1
• fac 4
• Returns 24

8
Embedding Tcl in Applications
Tcl
Application
Init
Parser
Command Loop
Built-In Commands
Application Commands

• Application generates Tcl scripts
• Tcl parses scripts, calls command procedures with
  argc, argv
• Application extends built-in command set
• define new object types in C
• implement primitive operations on objects as new
  Tcl commands
• build complex features with Tcl scripts

9
The Tk Toolkit

• Problem
• too hard to build applications with nice user
  interfaces
• Wrong Solution
• C, object-oriented toolkits
• only 10-20 improvement, must still program at
  low level
• Right Solution
• raise the level of GUI programming
• create interfaces by writing Tcl scripts

10
Creating Interfaces with Tk

• Widgets/windows have path names
• .dlg.quit
• Create widget with command named after class
• button .dlg.quit -text Quit \
• -foreground red -command exit
• Tell geometry manager where to display widget
• place .dlg.quit -x 0 -y 0
• pack .dlg.quit -side bottom

11
Other Tk Features

• Manipulate widgets with widget commands
• .dlg.quit flash
• .dlg.quit configure -relief sunken
• Use Tcl for interconnection
• buttons, menu entries invoke Tcl commands
• scrollbars and listboxes communicate with Tcl
• can define new event bindings in Tcl
• selection, focus accessible via Tcl
• Tk also provides C interfaces
• create new widget classes
• create new geometry managers

12
Whats a Tk-Based Application?

• 1. The Tcl interpreter
• 2. The Tk toolkit
• 3. Application-specific C code (primitives!)
• new object types
• new widgets
• 4. Tcl scripts (compose primitives)
• build GUI
• respond to events

Tcl commands
13
Wish Simplest Tk Application

• Wish - windowing shell
• No C code except command-line reader
• Can build many apps as wish scripts
• Hello, world
• label .hello \
• -text Hello, world
• .pack .hello
• simple directory browser
• 30 lines of Tk/Tcl

14
Browser Wish Script

• listbox .list -yscroll .scroll set \
• -relief raised -width 20 -height 20
• pack .list -side left
• scrollbar .scroll -command .list yview
• pack .scroll -side right -fill y
• if argc gt 0
• set dir lindex argv 0
• else
• set dir .
• foreach i exec ls -a dir
• .list insert end i
• bind .list ltDouble-Button-1gt
• browse dir selection get
• bind .list ltControl-cgt destroy .
• focus .list

15
Browse Script Cont.

• proc browse dir file
• global env
• if dir ! . set file dir/file
• if file isdirectory file
• exec browse file
• else
• if file isfile file
• exec env(EDITOR) file
• else
• puts stdout cant browse file
• Browse is also name of wish script

16
TkSol - Tk-Based Solitaire Program
17
TkSol Statistics

• Code
• 1635 lines of Tk/Tcl code
• 4 card down bitmaps
• 52 card up bitmaps (4 suits of 13 cards each)
• almost all time in bitmap creation
• Comparison to MS Solitaire
• simpler end game
• has auto-play mode
• slower startup
• slower deal
• similar interactive speed

18
TkMines Statistics

• Code
• 1178 lines of Tk/Tcl code
• uses a few signal and time commands from TclX
  extension, are not really needed
• several small bitmaps for squares
• Comparison to MS Mines
• simpler score file
• same look-and-feel
• slower startup
• similar interactive performance

19
Composing Applications

• Problem
• only communication between applications is via
  selection
• OLE on MS Windows provides object selection
• result monolithic programs
• Solution - send command
• send appName command
• any Tk application can invoke anything in any
  other Tk application interface or actions
• result powerful communication
• result big security hole

20
Composing Applications, cont.

• Examples
• debugger - sends command to editor to highlight
  line of execution
• UI editor - sends commands to modify interface of
  live application
• multimedia - send record, play commands to audio
  and video applications
• spreadsheets - cell sends commands to database to
  fetch current value
• Revolutionary results
• build complex systems as collections of
  specialized but reusable hypertools
• easy to create active objects embeddable Tcl
  commands. Hypertext, hypermedia is easy.

21
Status

• Source and documentation freely available
• developed at UC Berkeley
• now maintained and developed at Sun Labs
• code redistributable in commercial applications
• runs on UNIX, Windows, Mac
• Large user/developer community
• 50,000 worldwide
• comp.lang.tcl newsgroup
• many commercial products
• several books
• Many extensions available
• Tk is just one extension

22
Drawbacks

• Must learn new language
• substitution can be confusing
• Interpreted language has performance limits
• want a compiler for some applications
• want to avoid C programming
• dynamic compiler will provide at least 10x
  speedup
• Competition
• Visual Basic
• AppleScript
• Java/JavaScript

23
Conclusions

• High-level programming
• less to learn
• easy to learn
• build applications very quickly
• One interpretive language for everything
• extend and modify applications at run-time
• make many things work together
• Web programming/agent language?
• platform independent
• interpreted
• easily embedded
• secure