Free42: Unlimited-length strings and other type extensions

[Thomas Okken]

While working on the big stack logic in Free42, it occurred to me that it would be nice to add a few new types to the type system. What got me thinking along those lines are lists, which would be very useful for creating temporary backups of the entire stack, but another HP-42S type system limitation that would be useful to tackle are strings. Unlimited-length strings would be useful for storing algebraic equations, and of course it would be nice to be able to use indirect alpha addressing without the six-character limit getting in the way of addressing seven-character labels and variables.

Real scalars with attached units will also require an extension to the type system...

Regarding the unlimited-length strings, it seems like this could actually be done almost transparently, since the current six-character limit is only enforced by ASTO. That means that all that would be needed is an ASTO variant that stores the entire alpha register. There would have to be some changes behind the scenes to allow unlimited-length strings to be stored in matrices (and thus also in numbered registers), but as long as the behavior of the regular ASTO doesn't change, this shouldn't affect legacy code at all.

Thoughts?