[plt-scheme] Immutable mappings on symbols

From: Carl Eastlund (carl.eastlund at gmail.com)
Date: Thu Jan 13 15:55:18 EST 2005

Thanks, this looks like exactly what I'm looking for.

It seems to me the eq-hash-order and equal-hash-order units would
provide only approximate orderings, because different items can
(rarely) be given the same hash code by (eq-hash-code ...) and
(equal-hash-code ...).  Is this the case?  Or does the set unit do
something intelligent in the rare case that equality can be tested
where less-than cannot?


On Thu, 13 Jan 2005 21:18:11 +0100, Jens Axel Søgaard
<jensaxel at soegaard.net> wrote:
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> Carl Eastlund wrote:
>  > MzScheme provides mutable hash tables keyed by symbols - actually, by
>  > any data - but I can't find any functional mappings, i.e. where insert
>  > and remove operations produce new mappings and preserve their inputs. I've had many occasions to want lookups based
> on symbols and it would
>  > be nice to have the option of persistent data.  Is this present
>  > somewhere I've overlooked, or is this a feature that could be added?
> Galore provides persistent search trees.
>    <http://planet.plt-scheme.org/docs/soegaard/galore.plt/1/0/doc.txt>
>    <http://planet.plt-scheme.org/#galore.plt>
> Comments on how to improve the library are welcome.
> --
> Jens Axel Søgaard

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