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Re: Kickstarter for Emacs

From: Phil Hagelberg
Subject: Re: Kickstarter for Emacs
Date: Fri, 20 Apr 2012 17:10:33 -0700

On Thu, Apr 19, 2012 at 2:02 PM, Stefan Monnier
<address@hidden> wrote:
>> I'd happily contribute money to the development of the concurrency
>> branch, the xembed work, or immutable strings/data structures.
> Curious: what do you expect "immutable strings/data structures"
> to provide?

I have been thinking about implementing egal from Henry Baker's famous
equality paper[1] in Emacs Lisp, but it is not very practical unless
you can make certain guarantees of immutability. Knowing that two
mutable strings are currently equal is not nearly as useful as knowing
that they will always be equal, and indeed in a concurrent setting is
hardly useful at all. Being able to construct a list or string that is
a stable value (that is, guaranteed not to change) allows you to write
code that is referentially transparent and thus much easier to
understand and maintain.

But then again, there is so much extant code that works in terms of
mutable strings and lists that interoperating between pure code and
mutable-friendly code might be too burdensome. I was thinking about
immutability primarily in the context of a compiler that could target
Emacs Lisp, which is probably crazy. =)


[1] - http://home.pipeline.com/~hbaker1/ObjectIdentity.html

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