On Fri, 19 Jul 2013 09:34:41 -0400, John Gilmore wrote:
>
>Organizing a symbol table/dictionary by identifier length is an old
>idea. For example, the Lowry-Medlock FORTRAN H compiler, to which I
>have referred here before, kept one-, two-, three-, four-, five- and
>six-character identifiers is separate subdictionaries. ...
>
This strikes me as naive technology. Beyond regarding the length
as a first-level hash index, I see little value in distinguishing among
3-, 4-, 5-, and 6-character identifiers. Hashing and binary search
trees probably give better results.
>There is strong evidence, derived from studies of large samples of
>source programs, that single-character identifiers are both fewer and
>referenced much more frequently than longer identifiers, at least in
>languages in the FORTRAN-ALGOL tradition.
There's a strict upper bound on the former; fairly small unless
one admits Unicode.
> ... This probably reflects the
>contaminating influence of mathematical notation. (I have more than
>once been dismayed to see that COBOL programmers, who are largely free
>of this malign influence and who do not use subscripts/indices a lot,
>often give them long identifiers like
>'in-batch-subgroup-index-position' when they do use them.)
>
It's unclear which tradition you favor. Mathematical/scientific
notation tends to use single-character identifiers, to be
case-sensitive, and to admit characters from Greek, Hebrew, ...
alphabets ("ψ*", "ℵo") (Unicode, again). (We needn't discuss APL.)
I have on occasion refactored code to use longer identifiers, both
for internal documentation and to facilitate string searches for them.
Even in Rexx I place little value on the performance benefits of
single character identifiers. (I know; modern development
environments obviate the need for searching for identifiers as
strings, but such tools are not uniformly available.)
-- gil
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