tailcall - Replace the current procedure with another command

       The  tailcall  command  replaces  the  currently  executing procedure, lambda application, or method with
       another command. The command, which will have arg... 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:

              return [uplevel 1 [list command ?arg...?]]

       This command may not be invoked from within an uplevel into a  procedure  or  inside  a  catch  inside  a
       procedure or lambda.

       Compute the factorial of a number.

              proc factorial {n {accum 1}} {
                  if {$n < 2} {
                      return $accum
                  }
                  tailcall factorial [expr {$n - 1}] [expr {$accum * $n}]
              }

       Print the elements of a list with alternating lines having different indentations.

              proc printList {theList} {
                  if {[llength $theList]} {
                      puts "> [lindex $theList 0]"
                      tailcall printList2 [lrange $theList 1 end]
                  }
              }
              proc printList2 {theList} {
                  if {[llength $theList]} {
                      puts "< [lindex $theList 0]"
                      tailcall printList [lrange $theList 1 end]
                  }
              }

       call, recursion, tail recursion

Tcl                                                    8.6                                        tailcall(3tcl)

       tailcall - Replace the current procedure with another command

apply(3tcl), proc(3tcl), uplevel(3tcl)

tailcallcommand ?arg...?
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