LAmbda calculus evaluator (interactive)

[Tim Peters]

[Kragen Sitaker]
> ...
> Many years ago, Colby Kraybill suggested to me that it would be nice
> to have something similar for mathematical expressions --- something
> that would do nothing on its own, but would do the grunt-work involved
> in an action like "take the reciprocal of both sides" or "divide both
> the top and bottom by (x-1)".

Hyland Software's "Merlyn" program does that; see

    http://www.hylandsoftware.com/

It's based on a general term-rewriting system, and is programmable by the
end-user (indeed, almost all the builtin rules are exposed in files you can
edit too).  However, it's proprietary, costs money, source for the engine
itself is not available, and it works only on Windows.  I often use it
instead of, e.g., Macsyma, because the high-powered systems drive me nuts
with the pervasive & often unhelpful transformations they make in an
eyeblink; Merlyn never does anything unless it's told to.

Similar but weaker symbolic facilities can be found, e.g., in Dave
Gillespie's Emacs calc, and high-end HP calculators.

If the world were sane, they would have written all these things in Python
<wink>.

the-temptation-to-use-the-time-machine-is-often-overwhelming-ly y'rs  - tim