[dict] makes named parameters easy.

======
 proc example {a b args} {
   if {[llength $args] == 1} {
     set args [lindex $args 0] ;# work with unexpanded args
   }

   # establish defaults
   set args [dict merge {default value} $args]

   # use elements from dict
   fn [dict get $args parameter]


   # (dangerously) use args dict as variables
   dict with args {
      lappend parameter "END"
   }
 }
======

Alternatively, one can use an [array] to the same effect:

======
 proc example {a b args} {
   if {[llength $args] == 1} {
     set args [lindex $args 0] ;# work with unexpanded args
   }

   # establish defaults
   array set A {default value}
   # pour in supplied args
   array set A $args

   # use elements from A
   fn $A(parameter)

   # array elements are variables, so there is no need to unpack them explicitly.
   lappend A(parameter) "END"
 }
======
----

[slebetman]: Also see [optproc] for another take on [named parameters].

----
[SL] 9/9/08: This needs some more explanation.

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