Ian Clark wrote:
IC> Another thing I'd really like in J (and rookies shouldn't be allowed
IC> to ask such things) is something like the C++ "const". A way of
IC> locking down the name of a quantity so that it can't be changed during
IC> "the run", whatever that is -- at least not without raising an error.
Newbie! Such a thing actually exists in the early (open source)
J versions, called "given names". These were identifiers ending
in a colon:
% j7
J7 Copyright (c) 1990-1993, Iverson Software Inc. All Rights Reserved.
foo: =. 8
foo:
8
foo: =. 9
|not reassignable
| foo: =.9
foo:
8
0!:55 ]0
%
The very early versions wouldn't even let you erase a given name.
The first actual implementation of given names was in J version 3
(March 1991); Since version 5, you were allowed to erase a given
name (and re-introduce it with a new value).
Back at the time, all "lettered" primitives ended in a dot.
J Release 2 (the first commercial, non-source release) introduced the
first "letter-colon" primitives (a: D: L: p: q: t:, to be specific)
and dropped user-defined "given names" at the same time.
I don't know why given names were removed from the language.
Version 7 was the one which introduced locales and name_loc_
locatives, and things like "foo:_loc_" or "foo_loc_:" weren't
implemented at all or not as you would have expected. Perhaps there
was just too much ambiguity about "the end of a name" and the
facility too unused to keep bothering about it any further.
I really don't know.
Martin
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