SS: Python's alike range. The semantic should be exactly the same (and seems the more sensible for Tcl also).
Examples:
range 10 ;# => 0 1 2 3 4 5 6 7 8 9 range 10 20 ;# => 10 11 12 13 14 15 16 17 18 19 range 10 20 2 ;# => 10 12 14 16 18 range 20 10 -2 ;# => 20 18 16 14 12
Code:
# range ?start? end ?step? # # Python's alike range function. # Returns the [start,end) integer range. # # Example: # # foreach x [range 0 10] y [range 20 0 -2] { # puts "$x $y" # } proc range args { set l [llength $args] if {$l == 1} { set start 0 set step 1 set end [lindex $args 0] } elseif {$l == 2} { set step 1 foreach {start end} $args break } elseif {$l == 3} { foreach {start end step} $args break } else { error {wrong # of args: should be "range ?start? end ?step?"} } set result {} if {$start <= $end} { for {set j $start} {$j < $end} {incr j $step} { lappend result $j } } else { for {set j $start} {$j > $end} {incr j $step} { lappend result $j } } return $result }
I think the Tcl core should include the range command as proposed in my reference implementation (that's semantically equivalent to Python's) for the following reasons:
I'm ready to implement and TIP-fy it, but it's probably best to "sense" the Tclers ideas before to go forward. So, comments are very welcomed.
RS: Here's a minimal variant that only does step-width 1:
proc range {from to} { if {$to>$from} {concat [range $from [incr to -1]] $to} } % range 0 5 0 1 2 3 4 % range 1 6 1 2 3 4 5
DKF: Extending is easy.
proc range {from to {step 1}} { if {$to>$from} {concat $from [range [incr from $step] $to $step]} }
however this is inefficient. Better to do this:
proc range {from to {step 1}} { set res $from; while {$to>$from} {lappend res [incr from $step]}; return $res }
or even this, adapting to work with negative steps...
proc range {from to {step 1}} { set res $from while {$step>0?$to>$from:$to<$from} {lappend res [incr from $step]} return $res }
See also Integer range generator. LV When this topic first arose some time ago, the Python function was described to me as one in which the numbers were only generated as needed. That way, if one specified a range of a million, one got them, but didn't wait around for them or carry the penalty of the long list. That delayed generation of value functionality, generalized beyond integers, seems like something more useful for Tcl. It might be used for floats, alphas, etc.
Category Algorithmtcl-20041012.tar.gz