On approximately 11/25/2008 11:01 PM, came the following characters from
the keyboard of Gene:
On Nov 26, 1:29 am, Xah Lee <[EMAIL PROTECTED]> wrote:
comp.lang.lisp,comp.lang.functional,comp.lang.perl.misc,comp.lang.python,comp.lang.java.programmer
2008-11-25
Recently, Steve Yegge implemented Javascript in Emacs lisp, and
compared the 2 languages.
http://steve-yegge.blogspot.com/http://code.google.com/p/ejacs/
One of his point is about emacs lisp's lack of namespace.
Btw, there's a question i have about namespace that always puzzled me.
In many languages, they don't have namespace and is often a well known
sour point for the lang. For example, Scheme has this problem up till
R6RS last year. PHP didn't have namespace for the past decade till
about this year. Javascript, which i only have working expertise,
didn't have namespace as he mentioned in his blog. Elisp doesn't have
name space and it is a well known major issue.
Of languages that do have namespace that i have at least working
expertise: Mathematica, Perl, Python, Java. Knowing these langs
sufficiently well, i do not see anything special about namespace. The
_essence_ of namespace is that a char is choosen as a separator, and
the compiler just use this char to split/connect identifiers.
Although i have close to zero knowledge about compiler or parser, but
from a math point of view and my own 18 years of programing
experience, i cannot fathom what could possibly be difficult of
introducing or implementing a namespace mechanism into a language. I
do not understand, why so many languages that lacks so much needed
namespace for so long? If it is a social problem, i don't imagine they
would last so long. It must be some technical issue?
Could any compiler expert give some explanation?
Thanks.
Xah
∑http://xahlee.org/
☄
When multiple existing systems are combined, namespaces provide a
quick way to prevent name clashes.
While the above is true, and is a benefit of name spaces, it appears the
OP understands that issue, and is asking why languages without
namespaces don't add them.
Speaking as someone who has written a few small compiler
implementations, I'll just point out that when doing a particular
implementation, there are often times more interesting or pressing needs
to be achieved by the implementation.
Many languages have other scoping techniques that limit the need for
global names, thus sidestepping the need for explicit namespaces, by
reducing their benefits.
Some operating systems have limited the allowable length of global
(linkable) names, especially in the early days of a computing platform
(be it the early days of mainframes, minicomputers, or microcomputers
[now called personal computers, and more powerful than many of the early
mainframes]), which led to corresponding limits in the languages
available on such systems.
And, absent namespaces, the user is not left totally without
alternative. Many languages place no or large limits on identifier
length, so namespace can be simulated by using "module prefixes". When
it is known that namespaces are not available, large scale systems
written in those languages usually have a coding standard that suggests
using a prefix on all global names for each separable unit of the
program. The team of programmers for each separable program unit, then,
is free to innovate with names within the subset of all possible names
having the assigned, negotiated, or claimed prefix for their global
names. Non-global names are usually not required to have the prefix, as
scoping rules limit the visibility of those names, although, depending
on the language, it may be decided that certain non-global names still
use the prefix for some sort of consistency.
Languages that have limited length variable names (some versions of
Basic are restricted to single character names; some versions of other
languages have limited variables names to other lengths -- thinking
back, 3, 6, 8, and 31 come to mind -- either in total length or
significant length) are harder mediums in which to develop large-scale
projects. Newer versions of languages containing most of the
length-limited-names tend to increase the allowable length, and/or
introduce namespaces, or modules (which oftentimes produces multiple
namespaces as a side-effect).
Multi-purpose languages today are mostly designed to cross-platform,
have modular compilation facilities necessitating linking of global
names, and recognize the needs of separate compilation, linking, and
name collisions, and provide some mechanism for avoiding name
collisions, either namespaces, or modules that provide namespaces. Most
operating systems and linkers provide for long names. Life is good.
There are still throwbacks, and still small applications, and still
languages that don't offer such facilities.
--
Glenn -- http://nevcal.com/
===========================
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