proc - Create a Tcl procedure
proc name args body
The
proc command creates a new Tcl procedure named
name, replacing
any existing command or procedure there may have been by that name. Whenever
the new command is invoked, the contents of
body will be executed by
the Tcl interpreter. Normally,
name is unqualified (does not include
the names of any containing namespaces), and the new procedure is created in
the current namespace. If
name includes any namespace qualifiers, the
procedure is created in the specified namespace.
Args specifies the
formal arguments to the procedure. It consists of a list, possibly empty, each
of whose elements specifies one argument. Each argument specifier is also a
list with either one or two fields. If there is only a single field in the
specifier then it is the name of the argument; if there are two fields, then
the first is the argument name and the second is its default value. Arguments
with default values that are followed by non-defaulted arguments become
required arguments; enough actual arguments must be supplied to allow all
arguments up to and including the last required formal argument.
When
name is invoked a local variable will be created for each of the
formal arguments to the procedure; its value will be the value of
corresponding argument in the invoking command or the argument's default
value. Actual arguments are assigned to formal arguments strictly in order.
Arguments with default values need not be specified in a procedure invocation.
However, there must be enough actual arguments for all the formal arguments
that do not have defaults, and there must not be any extra actual arguments.
Arguments with default values that are followed by non-defaulted arguments
become de-facto required arguments, though this may change in a future version
of Tcl; portable code should ensure that all optional arguments come after all
required arguments.
There is one special case to permit procedures with variable numbers of
arguments. If the last formal argument has the name “
args”, then a call to the procedure may contain more actual
arguments than the procedure has formal arguments. In this case, all of the
actual arguments starting at the one that would be assigned to
args are
combined into a list (as if the
list command had been used); this
combined value is assigned to the local variable
args.
When
body is being executed, variable names normally refer to local
variables, which are created automatically when referenced and deleted when
the procedure returns. One local variable is automatically created for each of
the procedure's arguments. Other variables can only be accessed by invoking
one of the
global,
variable,
upvar or
namespace
upvar commands. The current namespace when
body is executed will be
the namespace that the procedure's name exists in, which will be the namespace
that it was created in unless it has been changed with
rename.
The
proc command returns an empty string. When a procedure is invoked,
the procedure's return value is the value specified in a
return
command. If the procedure does not execute an explicit
return, then its
return value is the value of the last command executed in the procedure's
body. If an error occurs while executing the procedure body, then the
procedure-as-a-whole will return that same error.
This is a procedure that takes two arguments and prints both their sum and their
product. It also returns the string “OK” to the caller as an
explicit result.
proc printSumProduct {x y} {
set sum [expr {$x + $y}]
set prod [expr {$x * $y}]
puts "sum is $sum, product is $prod"
return "OK"
}
This is a procedure that accepts arbitrarily many arguments and prints them out,
one by one.
proc printArguments args {
foreach arg $args {
puts $arg
}
}
This procedure is a bit like the
incr command, except it multiplies the
contents of the named variable by the value, which defaults to
2:
proc mult {varName {multiplier 2}} {
upvar 1 $varName var
set var [expr {$var * $multiplier}]
}
info(3tcl),
unknown(3tcl)
argument, procedure