NAME
proc - Create a Tcl procedure
SYNOPSIS
proc name args body
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DESCRIPTION
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 inter
preter. Normally, name is unqualified (does not include
the names of any containing namespaces), and the new pro
cedure is created in the current namespace. If name
includes any namespace qualifiers, the procedure is cre
ated in the specified namespace. Args specifies the for
mal arguments to the procedure. It consists of a list,
possibly empty, each of whose elements specifies one argu
ment. 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.
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 invok
ing command or the argument's default value. Arguments
with default values need not be specified in a procedure
invocation. However, there must be enough actual argu
ments for all the formal arguments that don't have
defaults, and there must not be any extra actual argu
ments. 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
formals. In this case, all of the actual arguments start
ing 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. Global variables can only be
accessed by invoking the global command or the upvar com
mand. Namespace variables can only be accessed by invok
ing the variable command or the upvar command.
dure is invoked, the procedure's return value is the value
specified in a return command. If the procedure doesn't
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.
SEE ALSO
info(n), unknown(n)
KEYWORDS
argument, procedure
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