Tornado

B
Tcl
B.2.7 Procedures
Procedure definition in Tcl is straightforward, and resembles many other
languages. The command proc builds a procedure from its arguments, which give
the procedure name, a list of its arguments, and a sequence of statements for the
procedure body. In the body, the return command specifies the result of the
procedure. For example, the following defines a procedure to compute the square
of a number:
B
proc square {i} {
return [expr $i * $i]
}
If a procedure’s argument list ends with the word args, the result is a procedure
that can be called with any number of arguments. All trailing arguments are
captured in a list $args. For example, the following procedure calculates the sum
of all its arguments:
proc sum {args} {
set accum 0
foreach item $args {
incr accum $item
}
return $accum
}
Defined Tcl procedures are called by name, and can be used just like any other Tcl
command. The following examples illustrate some possibilities:
Table B-8
Calling a Tcl Procedure
Tcl Expression
Result
square 4 16
square [sum 1 2 3] 36
set x "squ"
set y "are"
squ
are
$x$y 4 16
The technique illustrated by the last example—constructing a procedure name “on
the fly”—is used extensively by Tornado tools to group a set of related procedures.
The effect is similar to what can be achieved with function pointers in C.
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