'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH tailcall n 8.6 Tcl "Tcl Built-In Commands"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
tailcall \- Replace the current procedure with another command
.SH SYNOPSIS
\fBtailcall \fIcommand\fR ?\fIarg ...\fR?
.BE
.SH DESCRIPTION
.PP
The \fBtailcall\fR command replaces the currently executing procedure, lambda
application, or method with another command. The \fIcommand\fR, which will
have \fIarg ...\fR passed as arguments if they are supplied, will be looked up
in the current namespace context, not in the caller's. Apart from that
difference in resolution, it is equivalent to:
.PP
.CS
return [uplevel 1 [list \fIcommand\fR ?\fIarg ...\fR?]]
.CE
.PP
This command may not be invoked from within an \fBuplevel\fR into a procedure
or inside a \fBcatch\fR inside a procedure or lambda.
'\" TODO: sort out the mess with the [try] command!
.SH EXAMPLE
.PP
Compute the factorial of a number.
.PP
.CS
proc factorial {n {accum 1}} {
    if {$n < 2} {
        return $accum
    }
    \fBtailcall\fR factorial [expr {$n - 1}] [expr {$accum * $n}]
}
.CE
.PP
Print the elements of a list with alternating lines having different
indentations.
.PP
.CS
proc printList {theList} {
    if {[llength $theList]} {
        puts "> [lindex $theList 0]"
        \fBtailcall\fR printList2 [lrange $theList 1 end]
    }
}
proc printList2 {theList} {
    if {[llength $theList]} {
        puts "< [lindex $theList 0]"
        \fBtailcall\fR printList [lrange $theList 1 end]
    }
}
.CE
.SH "SEE ALSO"
apply(n), proc(n), uplevel(n)
.SH KEYWORDS
call, recursion, tail recursion
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