TCL PROC

Procedures are nothing but code blocks with series of commands that provide a specific reusable functionality. It is used to avoid same code being repeated in multiple locations. 

Procedures are equivalent to the functions used in many programming languages and are made available in Tcl with the help of proc command.

The syntax of creating a simple procedure is shown below −

proc procedureName {arguments} {

   body

}

 

      Procedure provides following benefits

         Easy maintenance – changes needs to be made only at one place

         Saves space, time and effort as a function is implemented only once

         Procedures can be shared when placed in “libraries”

           

A simple example for procedure is given below –

proc helloWorld {} {

   puts "Hello, World!"

}

helloWorld

When the above code is executed, it produces the following result −

Hello, World!

Procedures with Multiple Arguments

An example for procedure with arguments is shown below –

proc add {a b} {

   return [expr $a+$b]

}

puts [add 10 30]

When the above code is executed, it produces the following result –

40

Procedures with Variable Arguments

An example for procedure with arguments is shown below –

proc avg {numbers} {

   set sum 0

   foreach number $numbers {

      set sum  [expr $sum + $number]

   }

   set average [expr $sum/[llength $numbers]]

   return $average

}

puts [avg {70 80 50 60}]

puts [avg {70 80 50 }]

When the above code is executed, it produces the following result –

65

66

Procedures with Default Arguments

Default arguments are used to provide default values that can be used if no value is provided. An example for procedure with default arguments, which is sometimes referred as implicit arguments is shown below –

proc add {a {b 100} } {

   return [expr $a+$b]

}

puts [add 10 30]

puts [add 10]

When the above code is executed, it produces the following result −

40

110

Recursive Procedures

An example for recursive procedures is shown below –

proc factorial {number} {

   if {$number <= 1} {

      return 1

   }

   return [expr $number * [factorial [expr $number - 1]]]

}

puts [factorial 3]

puts [factorial 5]

When the above code is executed, it produces the following result −

6

120

4 ways to pass an arguments to procedure.

Pass by value

Proc sum {a b} {

Set num [expr $a + $b]

Puts “The sum is: $num”

}

Sum 2 3

Pass by name

Array set months {1 Jan 2 Feb}

Parray months                                                                                                                                

Or

Proc increase {initial_apy change} {

Upvar $initial_pay x

Foreach item [array names x] {

Set x($item) [expr $x($item) + $change]

}

}

Array set Pay {Ray Steve 50 Fred 200}

Increase Pay 25

Parray Pay

Defaults

Proc myprocdefault  {{}{}{}} {

Puts “$a $b $c”

}

Myprocdefault

Variable arguments

Proc show {a args} {

Puts $a

foreach val  $args {puts $val}

}

Show 1 2 3

Create a procedure that will accept one argument and variable arguments

proc variable {a args} {

puts $a

foreach val $args { puts $val }

}

variable 1 2 3 4 5

Output:

1

2

3

4

5

Example Variable number of arguments. 

proc args_parser {args} {

    set length [llength $args]

    puts "Length of the args is $length"

    for { set i 0 } { $i < $length } { incr i } {

        set arg_name [lindex $args $i]

        incr i

        set arguments($arg_name) [lindex $args $i]

    }

    return [array get arguments]

}

proc b {args} {

    array set ar [eval args_parser $args]

    set name $ar(-name)

    set age $ar(-age)

    set country $ar(-country)

    set location $ar(-location)

    puts "$name is aged $age\n";

    puts "$name is located at $location,$country\n";

}

b -name manish -age 27 -location bangalore -country India