Version 6 of tcl-null

Updated 2006-09-23 09:28:20 by suchenwi

Arising from a discussion (on Tcl chatroom about the denotational semantics of tcl, the concept of tcl-null was proposed.

MS offers this pragmatic approximation of tcl-null:

   set cmds [info command]
   rename catch _catch
   rename rename _rename
   foreach c $cmds {_catch {_rename $c {}}}
   _rename _catch {} 
   _rename _rename {}

but notes that namespaces also have to be cleaned up. - RS: You can have that, and all of the above: a brain-dead interpreter that understands no command any more, with

 namespace delete ::

tcl-null Game

Starting with this as a base, the game is to come up with minimal subset of built-in commands which provide a useful (if not exactly usable) language from which many of the facilities of tcl can be built.

CMcC Sat 23rd Sep 2006. One such set is apply set uplevel list lindex return. This resembles the minimal set of lisp functions necessary to construct classic lisp: (eval) (cond) (lambda) (quote) (car) and (cdr) from which McCarthy could construct/emulate classic-lisp. - RS: list is not needed in the set of fundamentals - the Tcl parser itself builds a list of the arguments before calling a command, so

 proc list args {return $args}

The above set constructs if as:

   proc if {c t f} {uplevel [lindex [list $t $f] [uplevel expr $cond]]}

The construction of proc or a near approximation is left as an exercise for the reader. :) MS says it can be done. I have no idea how. - RS Allowing for an extra interp command, proc is a special case of apply:

 proc f x {expr {$x*$x}}

is equivalent to

 interp alias {} f {} apply {x {expr {$x*$x}}}

dgp pointed out the need for return and also adds if your aim is to get back to the full Tcl built-in set, you'll need trace

This raises the question of the aim of the tcl-null game. I think there are three possible games:

  1. to construct a useful set
  2. to construct a usable set
  3. to construct the full Tcl built-in set.

[Category Concept]