tailcall(n) Tcl Built-In Commands tailcall(n)
NAME
tailcall - Replace the current procedure with another command
SYNOPSIS
tailcall command ?arg ...?
DESCRIPTION
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.
EXAMPLE
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]
} }
SEE ALSO
apply(n), proc(n), uplevel(n)
KEYWORDS
call, recursion, tail recursion
Tcl 8.6 tailcall(n)
tcl 8.6.0 - Generated Sun Jan 13 17:19:51 CST 2013