return(n) Tcl Built-In Commands return(n)______________________________________________________________________________NAMEreturn - Return from a procedure
SYNOPSISreturn ?-code code? ?-errorinfo info? ?-errorcode code? ?string?
_________________________________________________________________DESCRIPTION
Return immediately from the current procedure (or top-level command or
source command), with string as the return value. If string is not
specified then an empty string will be returned as result.
EXCEPTIONAL RETURN CODES
In addition to the result of a procedure, the return code of a proce‐
dure may also be set by return through use of the -code option. In the
usual case where the -code option isn't specified the procedure will
return normally. However, the -code option may be used to generate an
exceptional return from the procedure. Code may have any of the fol‐
lowing values:
ok (or 0) Normal return: same as if the option is omitted. The
return code of the procedure is 0 (TCL_OK).
error (1) Error return: the return code of the procedure is 1
(TCL_ERROR). The procedure command behaves in its calling
context as if it were the command error result. See below
for additional options.
return (2) The return code of the procedure is 2 (TCL_RETURN). The
procedure command behaves in its calling context as if it
were the command return (with no arguments).
break (3) The return code of the procedure is 3 (TCL_BREAK). The
procedure command behaves in its calling context as if it
were the command break.
continue (4) The return code of the procedure is 4 (TCL_CONTINUE). The
procedure command behaves in its calling context as if it
were the command continue.
value Value must be an integer; it will be returned as the
return code for the current procedure.
The -code option is rarely used. It is provided so that procedures
that implement new control structures can reflect exceptional condi‐
tions back to their callers.
Two additional options, -errorinfo and -errorcode, may be used to pro‐
vide additional information during error returns. These options are
ignored unless code is error.
The -errorinfo option specifies an initial stack trace for the error‐
Info variable; if it is not specified then the stack trace left in
errorInfo will include the call to the procedure and higher levels on
the stack but it will not include any information about the context of
the error within the procedure. Typically the info value is supplied
from the value left in errorInfo after a catch command trapped an error
within the procedure.
If the -errorcode option is specified then code provides a value for
the errorCode variable. If the option is not specified then errorCode
will default to NONE.
EXAMPLES
First, a simple example of using return to return from a procedure,
interrupting the procedure body.
proc printOneLine {} {
puts "line 1" ;# This line will be printed.
return
puts "line 2" ;# This line will not be printed.
}
Next, an example of using return to set the value returned by the pro‐
cedure.
proc returnX {} {return X}
puts [returnX] ;# prints "X"
Next, a more complete example, using return-code error to report
invalid arguments.
proc factorial {n} {
if {![string is integer $n] || ($n < 0)} {
return-code error \
"expected non-negative integer,\
but got \"$n\""
}
if {$n < 2} {
return 1
}
set m [expr {$n - 1}]
set code [catch {factorial $m} factor]
if {$code != 0} {
return-code $code $factor
}
set product [expr {$n * $factor}]
if {$product < 0} {
return-code error \
"overflow computing factorial of $n"
}
return $product
}
Next, a procedure replacement for break.
proc myBreak {} {
return-code break
}
SEE ALSObreak(n), catch(n), continue(n), error(n), proc(n), source(n),
tclvars(n)KEYWORDS
break, catch, continue, error, procedure, returnTcl 7.0 return(n)
