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| -rw-r--r-- | doc/return.n | 97 |
1 files changed, 49 insertions, 48 deletions
diff --git a/doc/return.n b/doc/return.n index 1f884e9..0137478 100644 --- a/doc/return.n +++ b/doc/return.n @@ -6,7 +6,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: return.n,v 1.12 2004/11/20 00:17:32 dgp Exp $ +'\" RCS: @(#) $Id: return.n,v 1.13 2007/10/25 09:49:18 dkf Exp $ '\" .so man.macros .TH return n 8.5 Tcl "Tcl Built-In Commands" @@ -21,7 +21,6 @@ return \- Return from a procedure, or set return code of a script .sp \fBreturn \fR?\fIoption value \fR...? ?\fIresult\fR? .BE - .SH DESCRIPTION .PP In its simplest usage, the \fBreturn\fR command is used without options @@ -41,14 +40,14 @@ will be returned as the result of the \fBsource\fR command. .PP In addition to the result of a procedure, the return code of a procedure may also be set by \fBreturn\fR -through use of the \fB-code\fR option. +through use of the \fB\-code\fR option. In the usual case where the \fB\-code\fR option isn't specified the procedure will return normally. However, the \fB\-code\fR option may be used to generate an exceptional return from the procedure. \fICode\fR may have any of the following values: .TP 13 -\fBok (or 0)\fR +\fBok (\fRor \fB0)\fR Normal return: same as if the option is omitted. The return code of the procedure is 0 (\fBTCL_OK\fR). .TP 13 @@ -78,7 +77,8 @@ were the command \fBcontinue\fR. return code for the current procedure. .LP When a procedure wants to signal that it has received invalid -arguments from its caller, it may use \fBreturn -code error\fR +arguments from its caller, it may use +.QW "\fBreturn \-code error\fR" with \fIresult\fR set to a suitable error message. Otherwise usage of the \fBreturn -code\fR option is mostly limited to procedures that implement a new control structure. @@ -86,8 +86,9 @@ procedures that implement a new control structure. The \fBreturn -code\fR command acts similarly within script files that are evaluated by the \fBsource\fR command. During the evaluation of the contents of a file as a script by \fBsource\fR, -an invocation of the \fBreturn -code \fIcode\fR command will cause -the return code of \fBsource\fR to be \fIcode\fR. +an invocation of the +.QW "\fBreturn -code \fIcode\fR" +command will cause the return code of \fBsource\fR to be \fIcode\fR. .SH "RETURN OPTIONS" .PP .VS 8.5 @@ -96,56 +97,56 @@ in Tcl also produces a dictionary of return options. In general usage, all \fIoption value\fR pairs given as arguments to \fBreturn\fR become entries in the return options dictionary, and any values at all are acceptable except as noted below. The \fBcatch\fR command may be -used to capture all of this information -- the return code, the result, -and the return options dictionary -- that arise from evaluation of a script. +used to capture all of this information \(em the return code, the result, +and the return options dictionary \(em that arise from evaluation of a script. .VE 8.5 .PP -As documented above, the \fB-code\fR entry in the return options dictionary +As documented above, the \fB\-code\fR entry in the return options dictionary receives special treatment by Tcl. There are other return options also recognized and treated specially by Tcl. They are: .TP -\fB-errorcode \fIlist\fR -The \fB-errorcode\fR option receives special treatment only when the value -of the \fB-code\fR option is \fBTCL_ERROR\fR. Then the \fIlist\fR value +\fB\-errorcode \fIlist\fR +The \fB\-errorcode\fR option receives special treatment only when the value +of the \fB\-code\fR option is \fBTCL_ERROR\fR. Then the \fIlist\fR value is meant to be additional information about the error, presented as a Tcl list for further processing by programs. -If no \fB-errorcode\fR option is provided to \fBreturn\fR when -the \fB-code error\fR option is provided, Tcl will set the value -of the \fB-errorcode\fR entry in the return options dictionary -to the default value of \fBNONE\fR. The \fB-errorcode\fR return +If no \fB\-errorcode\fR option is provided to \fBreturn\fR when +the \fB\-code error\fR option is provided, Tcl will set the value +of the \fB\-errorcode\fR entry in the return options dictionary +to the default value of \fBNONE\fR. The \fB\-errorcode\fR return option will also be stored in the global variable \fBerrorCode\fR. .TP -\fB-errorinfo \fIinfo\fR -The \fB-errorinfo\fR option receives special treatment only when the value -of the \fB-code\fR option is \fBTCL_ERROR\fR. Then \fIinfo\fR is the initial +\fB\-errorinfo \fIinfo\fR +The \fB\-errorinfo\fR option receives special treatment only when the value +of the \fB\-code\fR option is \fBTCL_ERROR\fR. Then \fIinfo\fR is the initial stack trace, meant to provide to a human reader additional information about the context in which the error occurred. The stack trace will also be stored in the global variable \fBerrorInfo\fR. -If no \fB-errorinfo\fR option is provided to \fBreturn\fR when -the \fB-code error\fR option is provided, Tcl will provide its own -initial stack trace value in the entry for \fB-errorinfo\fR. Tcl's +If no \fB\-errorinfo\fR option is provided to \fBreturn\fR when +the \fB\-code error\fR option is provided, Tcl will provide its own +initial stack trace value in the entry for \fB\-errorinfo\fR. Tcl's initial stack trace will include only the call to the procedure, and stack unwinding will append information about higher stack levels, but there will be no information about the context of the error within the procedure. Typically the \fIinfo\fR value is supplied from -the value of \fB-errorinfo\fR in a return options dictionary captured +the value of \fB\-errorinfo\fR in a return options dictionary captured by the \fBcatch\fR command (or from the copy of that information stored in the global variable \fBerrorInfo\fR). .TP -\fB-level \fIlevel\fR +\fB\-level \fIlevel\fR .VS 8.5 -The \fB-level\fR and \fB-code\fR options work together to set the return +The \fB\-level\fR and \fB\-code\fR options work together to set the return code to be returned by one of the commands currently being evaluated. The \fIlevel\fR value must be a non-negative integer representing a number of levels on the call stack. It defines the number of levels up the stack at which the return code of a command currently being evaluated should -be \fIcode\fR. If no \fB-level\fR option is provided, the default value +be \fIcode\fR. If no \fB\-level\fR option is provided, the default value of \fIlevel\fR is 1, so that \fBreturn\fR sets the return code that the current procedure returns to its caller, 1 level up the call stack. The mechanism by which these options work is described in more detail below. .VE 8.5 .TP -\fB-options \fIoptions\fR +\fB\-options \fIoptions\fR .VS 8.5 The value \fIoptions\fR must be a valid dictionary. The entries of that dictionary are treated as additional \fIoption value\fR pairs for the @@ -169,8 +170,8 @@ evaluation to terminate without evaluating all commands in sequence. Some of Tcl's built-in commands evaluate scripts as part of their functioning. These commands can make use of exceptional return codes to enable special features. For example, the built-in -Tcl commands that provide loops -- such as \fBwhile\fR, \fBfor\fR, -and \fBforeach\fR -- evaluate a script that is the body of the +Tcl commands that provide loops \(em such as \fBwhile\fR, \fBfor\fR, +and \fBforeach\fR \(em evaluate a script that is the body of the loop. If evaluation of the loop body returns the return code of \fBTCL_BREAK\fR or \fBTCL_CONTINUE\fR, the loop command can react in such a way as to give the \fBbreak\fR and \fBcontinue\fR commands @@ -180,16 +181,16 @@ their documented interpretation in loops. Procedure invocation also involves evaluation of a script, the body of the procedure. Procedure invocation provides special treatment when evaluation of the procedure body returns the return code -\fBTCL_RETURN\fR. In that circumstance, the \fB-level\fR entry in the +\fBTCL_RETURN\fR. In that circumstance, the \fB\-level\fR entry in the return options dictionary is decremented. If after decrementing, -the value of the \fB-level\fR entry is 0, then the value of -the \fB-code\fR entry becomes the return code of the procedure. -If after decrementing, the value of the \fB-level\fR entry is +the value of the \fB\-level\fR entry is 0, then the value of +the \fB\-code\fR entry becomes the return code of the procedure. +If after decrementing, the value of the \fB\-level\fR entry is greater than zero, then the return code of the procedure is \fBTCL_RETURN\fR. If the procedure invocation occurred during the evaluation of the body of another procedure, the process will repeat itself up the call stack, decrementing the value of the -\fB-level\fR entry at each level, so that the \fIcode\fR will +\fB\-level\fR entry at each level, so that the \fIcode\fR will be the return code of the current command \fIlevel\fR levels up the call stack. The \fBsource\fR command performs the same handling of the \fBTCL_RETURN\fR return code, which explains @@ -198,10 +199,10 @@ to \fBreturn\fR invocation within a procedure. .PP The return code of the \fBreturn\fR command itself triggers this special handling by procedure invocation. If \fBreturn\fR -is provided the option \fB-level 0\fR, then the return code +is provided the option \fB\-level 0\fR, then the return code of the \fBreturn\fR command itself will be the value \fIcode\fR -of the \fB-code\fR option (or \fBTCL_OK\fR by default). Any other value -for the \fB-level\fR option (including the default value of 1) +of the \fB\-code\fR option (or \fBTCL_OK\fR by default). Any other value +for the \fB\-level\fR option (including the default value of 1) will cause the return code of the \fBreturn\fR command itself to be \fBTCL_RETURN\fR, triggering a return from the enclosing procedure. .VE 8.5 @@ -223,14 +224,15 @@ proc returnX {} {\fBreturn\fR X} puts [returnX] ;# prints "X" .CE .PP -Next, a more complete example, using \fBreturn -code error\fR +Next, a more complete example, using +.QW "\fBreturn \-code error\fR" to report invalid arguments. .CS proc factorial {n} { if {![string is integer $n] || ($n < 0)} { - \fBreturn\fR -code error \\ - "expected non-negative integer,\\ - but got \\"$n\\"" + \fBreturn\fR -code error \e + "expected non-negative integer,\e + but got \e"$n\e"" } if {$n < 2} { \fBreturn\fR 1 @@ -242,7 +244,7 @@ proc factorial {n} { } set product [expr {$n * $factor}] if {$product < 0} { - \fBreturn\fR -code error \\ + \fBreturn\fR -code error \e "overflow computing factorial of $n" } \fBreturn\fR $product @@ -257,13 +259,13 @@ proc myBreak {} { .CE .PP .VS 8.5 -With the \fB-level 0\fR option, \fBreturn\fR itself can serve +With the \fB\-level 0\fR option, \fBreturn\fR itself can serve as a replacement for \fBbreak\fR. .CS interp alias {} Break {} \fBreturn\fR -level 0 -code break .CE .PP -An example of using \fBcatch\fR and \fBreturn -options\fR to +An example of using \fBcatch\fR and \fBreturn \-options\fR to re-raise a caught error: .CS proc doSomething {} { @@ -292,9 +294,8 @@ proc myReturn {args} { } .CE .VE 8.5 - .SH "SEE ALSO" -break(n), catch(n), continue(n), dict(n), error(n), proc(n), source(n), tclvars(n) - +break(n), catch(n), continue(n), dict(n), error(n), proc(n), source(n), +tclvars(n) .SH KEYWORDS break, catch, continue, error, procedure, return |