Expressiveness.

[David Collier-Brown]

In article <25930 at cca.CCA.COM> g-rh at CCA.CCA.COM.UUCP (Richard Harter) writes:
| ...  then there are programs of length N and execution time
| O(N) in language B such that any equivalent program in language A requires
| either O(N logN) execution time or O(n *exp(N)) space, or some combination
| thereof.  By this criteria the goto is more powerful than the while-loop.
| The hierarchy of strengths runs
| 
| 	while-loop
| 	forever-loop-with-multiple-escapes
| 	goto
| 	procedure-invocation-and-return
| 	computed-goto/switch
| 
| The switch construct is equivalent in power to the computed goto.
| 
| This measure of power is unambiguous.  One can also speak of the expressiveness
| of a construct, in the sense of what can be easily done in the language.
| Although this is probably the most useful criteria (and I suspect what you
| really) meant it is obviously vague and subjective.

  Ah, now that's interesting.
  I wonder if we can define a measure for expressiveness in like
terms, and judge fairly (at the "big-O" level) between them.

  I envisage something like
	expressiveness::= (to + from)
	to::= space (in characters) occupied by a given construct 
	from::= time (in character-transformations) to decompose the
		construct into its primitives
  Specifically, I see an if-else as
	to = "if (expression) { statement } else { statement }"
	   = 40 characters
	from = "(expression) ifgoto { statement goto } { statement }"
	   = 8 added + 4 removed 
           = 12 characters 
  Therefore an if-else costs 40 units to write, and 12 more units to
write/read as a transformation into simpler terms.

  Yes, I well realize I'm bullshitting with the character counting.
This is a proposed "proof of concept" of a rather fuzzy idea.

 --dave (try it on Dijkstra's if's and do's) c-b
-- 
 David Collier-Brown.                 {mnetor yunexus utgpu}!geac!daveb
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