'''Problem:''' it doesn't

A version number is:

   join $listOfNonNegativeIntegers .

Want to add recognition of things like ''8.4b1''

'''Concept:''' allow values -1 and -2 in the list.

Wherever the result has ''.-1.'' replace with ''b''

Wherever the result has ''.-2.'' replace with ''a''

'''Implies:''' ''a'' or ''b'' can't be next to a ''.''

''a'' or ''b'' can't be first or last char in version number

Things like ''1.2a5b3.7'' are OK (if weird)

'''Specification:'''

[[package vcompare]] extended obvious way (-2 < -1 < 0).

[[package vsatisfies]] -- need to specify sensible rules 
(for itself and to be used by [[package require]])

[[package vsatisfies 1.1 1.0]] => 1

[[package vsatisfies 1.1a0 1.0]] => 1

[[package vsatisfies 1.1b0 1.0]] => 1

'''Note:''' implies responsibility for controlling
package availability placed on package installer!
(Provide alpha/beta releases to developers, but hide
from end-users, for example -- special TCLLIBPATH, etc.)

[[package vsatisfies 1.1a1 1.1a0]] => ???

[[package vsatisfies 1.1b0 1.1a0]] => ???

[[package vsatisfies 1.1 1.1a0]] => ???

[[package vsatisfies 1.1b1 1.1b0]] => ???

[[package vsatisfies 1.1 1.1b0]] => ???

Also consider new cases when [package BoF: PACKAGE REQUIRE support for RANGES of acceptable versions] is present.

[['''package vsatisfies''' ''$version $range ?$range ...?'']]

----

Why stop to a and b?

======
 proc vsplit {ver} {
  if {![regexp {^\d+($|(.\d+|[a-z]{1}(\d+|$))*)$} $ver]} {error "expected version number but got \"$ver\""}
  set r {}
  foreach {a b c d e} [regexp -all -inline {(\d+)[.$]?|([a-z])($|(\d+))} $ver] {
   if {$b ne {}} {lappend r $b} else {
    lappend r [expr {[scan $c %c]-123}]
    if {$d ne {}} {lappend r $d}
   }
  }
  return $r
 }
 
 proc vcompare {uv vv} {
  set uv [vsplit $uv]
  set vv [vsplit $vv]
  if {[set m [llength $uv]] > [llength $vv]} {
   lappend vv {*}[lrepeat [expr {$m-[llength $vv]}] 0]
  } elseif {[set m [llength $vv]] > [llength $uv]} {
   lappend uv {*}[lrepeat [expr {$m-[llength $uv]}] 0]
  }
  for {set i 0} {$i < $m} {incr i} {
   if {[lindex $uv $i] < [lindex $vv $i]} {return -1}
   if {[lindex $uv $i] > [lindex $vv $i]} {return 1}
  }
  return 0
 }
======

I wrote this because I needed something like this. So far it has worked, but I haven't tested it a lot. Or at all.

It does:
   * allow letters in version numbers (''1.2a'', ''1.2a5'', ''1.2a5b3.7'', ''0.59r'')
   * conform to [[package vcompare]] even to extent of error message
   * '''not''' allow a letter to be followed by a letter, or version number to start with anything but a number
   * require 8.5 due {*} and [[lrepeat]]
   * bite the bullet in performance and elegance, probably.

Just to make my second appearance in this great Wiki,

-Kaitzschu.

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