TCL

1
TCL

• Tool Command Language

2
About

• Scripting language
• Functional, but not completely
• Imperative
• Object oriented
• Logical?
• Similarities
• C
• Shell
• LISP

3
Syntax Vocabulary

• Script
• A string that is a sequence of commands,
  separated by newlines or semicolons.
• Command
• A string that is a list of words, separated by
  blanks.
• Word
• A string that is a simple word, or one that
  begins with and ends with the matching , or
  one that begins with and ends with the matching
  .

4
Syntax 11 Rules

• Words
• Commands
• Evaluation
• Double Quotes
• Braces
• Command Substitution
• Variable Substitution
• Backslash Substitution
• Order of Substitution
• Substitution and word boundaries
• Comments

5
Rule 1 Words

• Strings
• Arbitrary in length
• Consist of nearly any characters
• Separated by White Space
• Except when quoted
• Example
• set a 3 contains 3 words (set, a, 3)
• this is one word treated as single word

6
Rule 2 Commands

• separated by newlines and semicolons.
• consist of one or more word
• First word is name of command
• Successive words are arguments
• Words can be command with around them
• Example
• set variable 3 variable 3
• expr 3 4 7
• set variable expr 3 4 variable 7

7
Rule 3 Evaluation

• Two step command evaluation
• Breaks command into words
• Performs substitution
• Single pass
• No meaning given yet

8
Rule 4 Double Quotes

• Special character are treated as ordinary
  characters
• semicolons, close brackets, white space, etc
• Double quotes not part of actual word.
• All types of Substitutions takes place

9
Rule 5 Braces

• String
• Anything inside has literal translation
• Braces not part of the word
• If braces inside quote, quoting rule applies
• No substitutions are performed
• Example
• set a literal str a literal str
• set b /non-a b non-literal str

10
Rule 6 Command Substitution

• If word inside of
• Evaluated recursively
• Example
• set a expr 34 a 347
• set b expr a incr a b
  7 (7 1) 7 8 15

11
Rule 7 Variable Substitution

• Variable begin with
• Variables can be nearly anything
• Letter, digit, underscore, etc.
• Example
• set a expr 11 puts 1 2 a
  1 2 2
• set 4 3 puts 4 3
• set two words one put two words
  one
• set array(0) 3 set i 0 puts
  array(i) 3

12
Rule 8 Backslash Substitution

• Similar to how it is used in Java
• Examples
• puts hello \\ world hello \ world
• puts price \350 price 3.50
• \a ltplays a soundgt
• puts \ \

13
Rule 9 Order of Substitution

• Processed
• One at a time
• Left to right
• Example
• set y set x 0incr xincr x y 012

14
Rule 10 Substitution and word boundaries

• Substitution doesnt effect word bounds
• Example
• set a one word put still a still one
  word
• The solution contains two words still, one
  word

15
Rule 11 Comments

• Use hash ()
• Must be at beginning of line
• Example
• comment
• set a comment
• set a NOT comment

16
Flow of Control

• If, For, Foreach, While
• All Commands
• Similar semantics to C
• Example
• If cond scriptA else scriptB

17
Procedures

• Local scope
• Customable
• Helps structure programs
• Example
• proc ! n if n 1 then return 1 else
  return expr n ! expr n-1
• ! 3 3! 3 2 1 6

18
Features

• proc solve a b return expr a b
• solve 2 3
• wrong args should be "solve a b
• solve 3 2
• 5

19
Features

• proc solve a op b return expr a op b
• solve 1 1
• 2
• solve 3 2
• 1
• solve 3 gt 1
• 1 (true)

20
Features

• rename expr solve
• solve 3 4
• 7
• solve 3 2
• 1

21
Feature

• proc do body while expression uplevel
  body while uplevel expr expression
  uplevel body set i 0 do
  puts i incr i while i lt 3
• 0
• 1
• 2