MC, 31 Dec 2004: In a post on his blog[L1 ] discussing implementation and design issues of his Ramble game (written, naturally in Tcl/Tk), WHD proposes a fori command, whose signature looks like:
fori var from to script
Since any Tcl version is going to be slower than the built-in version of [for], Will writes: "I think something like fori would be a nice addition to Tcl...but it would have to be implemented as a C extension."
Here are a couple of different approaches I came up with this afternoon:
proc fori1 {var m n script} {
uplevel 1 for [list "set [list $var] $m"] [list "\$[list $var] <= $n"] [list "incr [list $var]"] [list $script]
}
proc fori2 {var m n script} {
uplevel 1 for [list "set [list $var] $m"] [list "\[set [list $var]\] <= $n"] [list "incr [list $var]"] [list $script]
}
proc fori3 {var m n script} {
uplevel 1 "set [list $var] [expr {$m - 1}]
while {\[incr [list $var]\] <= {$n}} {
$script
}"
}
proc fori4 {var m n script} {
uplevel 1 "if {1} {
for {set [list $var] {$m}} {\$[list $var] <= {$n}} {incr [list $var]} {
$script
}
}"
}
proc fori5 {var m n script} {
uplevel 1 "if {1} [list "set [list $var] [expr {$m - 1}]
while {\[incr [list $var]\] <= {$n}} {
$script
}"]"
}
and now a bit of infrastructure to make testing/timing them easier:
proc try {name proc limit {n_iterations 1}} {
set time [time {set result [$proc $limit]} $n_iterations]
return [format { #%-5s %-14s result == %8d, in %7d microseconds} \
$name "(1 .. $limit):" $result [lindex $time 0]]
}
proc builtin {limit} {
set sum 0
for {set i 1} {$i <= $limit} {incr i} {
incr sum $i
}
return $sum
}
for {set i 1} {$i <= 5} {incr i} {
proc method$i {limit} [format {
set sum 0
fori%d i 1 $limit {incr sum $i}
return $sum
} $i]
}
foreach size {10 100 1000 10000} {
if {$size != 10} then {puts ""}
foreach version {builtin method1 method2 method3 method4 method5} \
name {for fori1 fori2 fori3 fori4 fori5} {
puts [try $name $version $size]
}
}and now to see the timing results (these are from tclsh 8.4.7 on a 1.33GHz PowerBook running MacOS X 10.3):
#for (1 .. 10): result == 55 in 47 microseconds #fori1 (1 .. 10): result == 55 in 297 microseconds #fori2 (1 .. 10): result == 55 in 3690 microseconds #fori3 (1 .. 10): result == 55 in 188 microseconds #fori4 (1 .. 10): result == 55 in 140 microseconds #fori5 (1 .. 10): result == 55 in 147 microseconds #for (1 .. 100): result == 5050 in 75 microseconds #fori1 (1 .. 100): result == 5050 in 3605 microseconds #fori2 (1 .. 100): result == 5050 in 1413 microseconds #fori3 (1 .. 100): result == 5050 in 933 microseconds #fori4 (1 .. 100): result == 5050 in 559 microseconds #fori5 (1 .. 100): result == 5050 in 521 microseconds #for (1 .. 1000): result == 500500 in 5557 microseconds #fori1 (1 .. 1000): result == 500500 in 11434 microseconds #fori2 (1 .. 1000): result == 500500 in 8427 microseconds #fori3 (1 .. 1000): result == 500500 in 6787 microseconds #fori4 (1 .. 1000): result == 500500 in 5049 microseconds #fori5 (1 .. 1000): result == 500500 in 1546 microseconds #for (1 .. 10000): result == 50005000 in 6567 microseconds #fori1 (1 .. 10000): result == 50005000 in 55847 microseconds #fori2 (1 .. 10000): result == 50005000 in 57480 microseconds #fori3 (1 .. 10000): result == 50005000 in 40697 microseconds #fori4 (1 .. 10000): result == 50005000 in 22051 microseconds #fori5 (1 .. 10000): result == 50005000 in 17589 microseconds
Out of these fori5 looks the best. In the 1-1000 range it is ~3x faster than for, and in the 1-10000 range it is only ~3x slower.
Please, feel free to add improved versions.