Version 1 of Factorial Using Event Loop

Updated 2003-10-01 08:09:12

I'm easily amused (especially when amusing myself). See Tail call optimization for other variations.

 proc continue: {args} {
    after idle $args
 }

 proc fac {n result {accum 1}} {
    if {$n > 1} {
        continue: fac [expr {$n-1}] $result [expr {$accum * $n}]
    } else {
        upvar $result res
        set res $accum
    }
 }

 fac 10 ::foo
 vwait ::foo
 puts $::foo

Hey, and there is room for more things to be done while calculating...

 proc do_ntimes {cnt code} {
    uplevel $code
    if {$cnt > 0} {
        continue: do_ntimes [incr cnt -1] $code
    }
 }

 fac 10 ::foo
 do_ntimes 10 {puts "hello world"}
 vwait ::foo
 puts $::foo

-- Todd Coram

---

RS Interesting: this is using the event queue instead of the recursion stack (which has a fixed depth limit - does the event queue have a similar limit?). Functional programmers will of course abhor procedures which do not return a value, as they are run asynchronously, and so mostly global variables will have to be used. But still - another cool braintwister...