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(3tcl), proc(3tcl), uplevel(3tcl)
KEYWORDS¶
call, recursion, tail recursion