Programming Using TclTk

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Programming Using Tcl/Tk

• Dr. Ernest J. Friedman-Hill
• ejfried_at_herzberg.ca.sandia.gov
• http//herzberg.ca.sandia.gov/

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• Programming productivity may be increased as
  much as five times when a suitable high-level
  language is used.
• F.P.Brooks, The Mythical Man-Month
• representation is important, because how
  information is represented can greatly affect how
  easy it is do do different things with it.
• David Marr, Vision

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Your Instructor

• SMTS in Scientific Computing at Sandia National
  Labs
• Writing Tcl code since Fall 1994
• Ph.D. in Chemistry, MIT 1992
• Using Tcl/Tk for systems integration, automated
  test, distributed computing
• Wrote XCELL Design Environment
• Friedman-Hill, E.J. and J.M. OConnor, The XCELL
  Integrated Product Realization Environment A
  Toolbox for Agile Construction of Custom
  Parametric Design Software, Proceedings of the
  1996 Agility Forum National Meeting, Boston, MA.

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What youll need

• A computer with WWW FTP access
• (UNIX preferred Win95, Win3.1 PC or Mac OK)
• Netscape Navigator (if available) for Tclets
• A Tcl/Tk installation
• http//www.sunlabs.com/research/tcl/install.html
• Binaries and source
• Textbook
• Ousterhouts Tcl and the Tk Toolkit
• (Addison-Wesley, ISBN 0-201-63337-X)
• Other reading material
• Up-to-date man pages Tk4.0 Porting document

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Other References

• Exploring Expect, Don Libes (O'Reilly, ISBN
  1-56592-090-2)
• Recommended reading.
• Practical Programming in Tcl and Tk, Brent Welch
  (Prentice Hall, ISBN 0-13-182007-9)
• Lots of examples. Comes with a source disk.
• http//www.sunlabs.com/research/tcl/
• Tcl/Tk home page. Source, docs, info.
• http//www.sunlabs.com/research/tcl/plugin/
• Home page for the new Navigator plug-in

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Who you are

• Write on a piece of paper
• Your name
• What you do
• What you want to do with Tcl/Tk
• What other computer languages you know
• Anything youd especially like to see covered

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What Ill do

• Today give an overview of the Tcl language
• Next four weeks
• Using the Tcl language
• GUI development with Tk
• Important Tcl extensions like expect
• Integrating Tcl/Tk with C and C applications
• Writing Tclets for the WWW
• Put course notes on the Web
• http//herzberg.ca.sandia.gov/TclCourse/
• PowerPoint format only (sorry)

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What youll do

• Complete several small problem sets
• Coding problems and questions
• Complete a term programming project
• You should choose a small application that fills
  a real need or solves a real problem
• Examples GUI for a command-line utility task
  automation a game or puzzle
• Briefly present your project at the last meeting
• Ask questions
• Participation in class or via email is expected

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Grading System

• Grade
• 40 Homework
• 40 Project
• 20 Participation
• Scores (None), OK, Good, Excellent
• Grading on a Curve. Mode is B.

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Overview of Tcl/Tk

• Component technologies
• Tcl embeddable scripting language
• Tk GUI toolkit and widgets based on Tcl.
• The principle universal scripting language
  controls everything functions, interfaces,
  communication.
• Results
• Raise the level of GUI programming simpler,
  5-10x faster application development than X, raw
  Win32
• Greater power programmable applications work
  together cross-platform delivery
• Active objects replace data with scripts.

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Outline

• Tcl scripting language.
• Tk toolkit.
• Tk applications.
• Survey of applications and extensions.
• Conclusions.

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Tcl Tool Command Language

• Interactive programs need command languages
• Typically redone for each application.
• Result weak, quirky.
• emacs and csh powerful, but can't reuse.
• Solution reusable scripting language.
• Interpreter is a C library.
• Provides basic features variables, procedures,
  etc.
• Applications extend with additional features.

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Scripting Language Philosophy

• Large, complex applications
• Performance important.
• Need structure.
• Goal prevent bad things.

• Interactive commands, scripting
• Performance less important.
• Minimum structure less overhead, easy
  interchange.
• Goal enable good things.

One language can't meet all needs?
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Two-Language Approach
Program size, complexity, reuse
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C
Tcl

• Use Tcl for scripting, C or C for large things.
• Goals for Tcl
• Minimal syntax easy to learn and type.
• Minimal structure make things play together.
• Simple interfaces to C extensibility.

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Tcl Tool Command Language

• Simple syntax (similar to sh, C, Lisp)
• set a 47 ? 47
• Substitutions
• set b a ? 47
• set b expr a10 ? 57
• Quoting
• set b "a is a" ? a is 47
• set b expr a10 ? expr a10

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More On The Tcl Language

• Rich set of built-in commands
• Variables, associative arrays, lists.
• C-like expressions.
• Conditionals, looping
• if "x lt 3"
• puts "x is too small"
• Procedures.
• Access to files, subprocesses, network sockets

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More On The Tcl Language

• Only data representation is zero-terminated
  strings
• Easy access from C.
• Programs and data interchangeable.
• set cmd1 "exec notepad"
• ...
• eval cmd1
• (notepad.exe launches under Windows)
• Unfortunately, no 8-bit data

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Factorial Procedure

• Defining and using procedures is easy!
• proc fac x
• if xlt1 return 1
• expr xfac expr x-1
• fac 4 ? 24

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Embedding Tcl In Applications

• Application generates scripts.
• Tcl parses scripts, passes words to command
  procedures.
• Application extends built-in command set
• Define new object types in C.
• Implement primitive operations as new Tcl
  commands.
• Build complex features with Tcl scripts.

Tcl
Application
Init
Command Loop
Parser
Application Commands
Built-In Commands

• Note that the command loop can also be in the
  Tcl/Tk box.

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Extensions
Tcl
Application
Extension
Init
Command Loop
Parser
Application Commands
Built-In Commands
Extension Commands

• Extensions can be developed independently
• Network communication, database access, security,
  ...
• Applications can include combinations of
  extensions.

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The Tk Toolkit

• The problem
• Too hard to build applications with nice user
  interfaces.
• Even harder to do so cross-platform
• The wrong solution
• C, object-oriented toolkits, Javas AWT
• Only small improvement (10-20?) must
  stillprogram at a low level.
• The right solution
• Raise the level of programming.
• Create interfaces by writing Tcl scripts.

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Creating User Interfaces With Tk

• Additional Tcl commands
• Create Motif-like widgets (on all platforms)
• Arrange widgets.
• Bind events to Tcl commands.
• Manipulate selection, focus, window manager, etc.
• Library of C procedures
• Create new widget classes.
• Create new geometry managers.

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What's A Tk-Based Application?

• The Tcl interpreter.
• The Tk toolkit.
• Optionally, application-specific C code
  (primitives)
• New commands.
• New widgets.
• Tcl scripts (compose primitives into actions)
• Build user interface.
• Respond to events.

Tcl commands
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Wish Windowing Shell

• Create user interfaces by writing Tcl scripts.
• Hello, world
• button .hello -text "Hello, world" -command exit
• pack .hello
• Simple directory browser 30 lines
• Web browser 2000 lines
• 10x less code for simple things.

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Browser Wish Script

• !/usr/local/bin/wish4.0
• listbox .list -yscroll ".scroll set" \
• -width 20 -height 20
• pack .list -side left
• scrollbar .scroll -command \
• ".list yview"
• pack .scroll -side right -fill y
• wm title . "File Browser"
• if argc gt 0
• set dir lindex argv 0
• else
• set dir .
• foreach i lsort glob .
• .list insert end i

• bind .list ltDouble-ButtonPress-1gt
• browse dir selection get
• bind all ltControl-cgt destroy .
• proc browse dir file
• if dir ! "."
• set file dir/file
• if file isdirectory file
• exec browse file
• else
• if file isfile file
• exec emacs file
• else
• error "can't browse file"

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Other Uses For Tcl

• Data representation
• Store data on disk as Tcl scripts.
• To load information, evaluate script
• Good for app configuration
• Active objects
• Store scripts in objects.
• Evaluate scripts to give objects behavior.
• Communication send Tcl scripts between
  applications.
• Executable content
• Active e-mail messages (Safe-Tcl)
• Web pages (Tclets)

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Status

• Runs on all UNIX/X platforms.
• Runs on Win32/Win16/Mac as of version 7.4/4.1.
• Source and documentation freely available.
• New Netscape Plug-In may increase audience.
• 100,000 developers world-wide?
• Hundreds of commercial products, free extensions.
• Newsgroup comp.lang.tcl.
• 2 introductory books (Ousterhout, Welch).

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Representative Applications

• Multimedia, groupware.
• Active e-mail messages.
• System administration.
• Testing.
• Scientific applications instrument control,
  simulation, visualization, CAD.
• Real-time control system for offshore platform.
• British teletext system.
• Feature animation at Walt Disney Studios.
• On-air broadcast control system for NBC.

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Popular Extensions

• Expect remote control for interactive UNIX
  programs such as ftp, telnet, crypt, and fsck
• !/usr/local/bin/expect
• spawn rlogin lindex argv 0
• expect -re "() "
• send "cd pwd\r"
• expect -re "() "
• send "setenv DISPLAY env(DISPLAY)\r"
• interact
• Expect is available via anonymous FTP
• ftp//ftp.cme.nist.gov/pub/expect/

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Popular Extensions, cont'd

• Archives via anonymous FTP
• ftp//ftp.neosoft.com/pub/tcl
• TclX general-purpose extensions
• POSIX system calls.
• Keyed lists.
• File scanning (similar to awk).
• Date/time manipulation.
• Debugging, help, profiling.
• Oratcl and Sybtcl access to commercial
  databases.
• Incr tcl object-oriented programming in Tcl.

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Popular Extensions, cont'd

• Tcl-DP socket-based remote procedure calls,
  distributed objects
• Sample unique ID server
• set myId 0
• proc GetId
• global myId
• incr myId
• return myId
• dp_MakeRPCServer 4545
• Sample client
• set server dp_MakeRPCClient foo.bar.com 4545
• dp_rpc server GetId
• Not yet updated for Tcl 7.4/4.1 socket command

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Where You Might Use Tcl and Tk

• Creating graphical user interfaces.
• Testing.
• Applications that need scripting or extension
  facilities.
• Platform-independent applications.
• Creating interactive content for the WWW.

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Drawbacks

• Must learn new language
• Substitution rules confusing to some people.
• Competitors JavaScript, Visual Basic
• Interpreted language has performance limits
• Surprisingly high not much worse than Java
• C interfaces incompatible with Xt, Motif library.
• Motif look-and-feel on PC, Mac for now.

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Whats up at Sun Labs?

• Create exciting Internet applications
• Netscape Plug-In available now!
• Increase accessibility
• More work on PC/Mac ports (native look and feel).
• SpecTcl interactive GUI builder (available now)
• Better development tools (debugger, etc.)
• Improving the language/toolkit
• Incremental on-the-fly compiler (some progress)
• Better support for modules, data structures.
• Dynamically loadable extensions now possible

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Summing up...

• High-level programming
• Less to learn.
• Build applications more quickly.
• Universal scripting language
• Extend and modify applications at run-time.
• Make many things work together.
• Use scripts instead of data
• Active objects, executable content.
• Tcl Tk shell of the 1990's?

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Tcl Language Programming

• There are two parts to learning Tcl
• 1. Syntax and substitution rules
• Substitutions simple, but may be confusing at
  first.
• 2. Built-in commands
• Can learn individually as needed.
• Control structures are commands, not language
  syntax.
• TCL HAS NO FIXED GRAMMAR!

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Basics

• Tcl script
• Sequence of commands.
• Commands separated by newlines, semi-colons.
• Tcl command
• One or more words separated by white space.
• First word is command name, others are arguments.
• Returns string result.
• Examples
• set a 22 set the variable a to 22
• puts "Hello, World!" worlds shortest program

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Division Of Responsibility
Command

• Chops commands into words.
• Makes substitutions.
• Does not interpret values of words.
• Single pass operation!

Tcl Parser
Words

• Interprets words.
• Can invoke parser recursively.
• Produces string result.

Command Procedure
Result
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Arguments

• Parser assigns no meaning to arguments (quoting
  by default, evaluation is special)
• C x 4 y x10
• y is 14
• Tcl set x 4 set y x10
• y is "x10"
• Different commands assign different meanings to
  their arguments. Type-checking must be done by
  commands themselves.
• set a 122
• expr 24/3.2
• eval "set a 122"
• button .b -text Hello -fg red
• string length Abracadabra

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Variable Substitution

• Syntax varName
• Variable name is letters, digits, underscores.
• This is a little white lie, actually.
• May occur anywhere in a word.
• Sample command Result
• set b 66 66
• set a b b
• set a b 66
• set a bbb 666666
• set a b.3 66.3
• set a b4 no such variable

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Command Substitution

• Syntax script
• Evaluate script, substitute result.
• May occur anywhere within a word.
• Sample command Result
• set b 8 8
• set a expr b2 10
• set a "b-3 is expr b-3" b-3 is 5

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Controlling Word Structure

• Words break at white space and semi-colons,
  except
• Double-quotes prevent breaks
• set a "x is x y is y"
• Curly braces prevent breaks and substitutions
• set a expr bc
• Backslashes quote special characters
• set a word\ with\ \\ and\ space
• Backslashes can escape newline (continuation)
• Substitutions don't change word structure
• set a "two words"
• set b a

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Notes on Substitution and Parsing

• Tcl substitution rules are simple and absolute
• Example comments
• set a 22 set b 33 lt- OK
• this is a comment lt- OK
• set a 22 same thing? lt- Wrong!
• set a 22 same thing lt- OK
• Parser looks at a command just once!
• Its OK to experiment
• Expressions exist that cant be written in one
  command
• Sometimes things get hairy cmd

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For Next Week...

• Get your Tcl/Tk environment set up
• Try the demos, especially Tks widget
• Type in Hello, World and get it to work
• Read Chapters 1 through 5 of Ousterhout