[GPS] Wed Jun 12, 2002: The code below implements a proc-like command that allows default values for arguments, and type checking of values given to arguments.

Comments and improvements are welcome.
----
  #! /bin/tclsh8.3
  
  #version 2
  proc ObjectProcInstanceCmd {argTable body argsPassed} {
    array set ar {}
  
    foreach arg $argTable {
      foreach {var value class} $arg break
      set ar($var) $value
      foreach alias [list nil empty string] {
        if {[string equal $alias $class]} {
          set class none
          break
        }
      } 
      set ar($var,class) $class
    }
  
    foreach {var value} $argsPassed {
      if {[info exists ar($var)] != 1} {
        return -code error "invalid flag: $var"
      }
  
      if {[string equal $ar($var,class) "none"] || [string is $ar($var,class) $value]} {
        set ar($var) $value
      } else {
        return -code error "invalid value: $value for flag: $var"
      }
    }
  
    eval $body
  }
  
  proc ObjectProc {name argStr label body} {
    set argTable [split $argStr \n]
  
    for {set i 0} {$i < [llength $argTable]} {incr i} {
      set arg [lindex $argTable $i]
      if {[string trim $arg] == ""} {
        set argTable [lreplace $argTable $i $i]
        continue
      }
  
      if {[llength $arg] != 3} {
        return -code error "received a bad argument table"
      }
    }
  
    proc $name {args} "ObjectProcInstanceCmd [list $argTable $body] \$args"
  }

----
'''Test code'''
  
  ObjectProc p {
    -x "" digit
    -y 20 digit
    -text "" none
  } body {
    puts "x + y [expr {$ar(-x) + $ar(-y)}]"
    puts "-text is $ar(-text)"
  }
  
  p -x 1 -y 20 -text "Hello World"
  p -x 5 -text Wonderment
  
  ObjectProc p2 {
    -width 256 digit
    -height 256 digit
    -title default string
  } body {
  
    puts "making a box named $ar(-title) that is $ar(-width) wide and $ar(-height) pixels tall"
  }
  
  p2
  p2 -title Boxy
  if 0 {
    #tests designed to fail
    catch {p2 -title Kablamo -width abc} res
    puts $res
    catch {p2 -tit} res
    puts $res
  }
----
'''Example output'''
x + y 21
-text is Hello World
x + y 25
-text is Wonderment
making a box named default that is 256 wide and 256 pixels tall
making a box named Boxy that is 256 wide and 256 pixels tall
----
[Category Command]