anybody have an opinion on how to get a language + extensive libraries
that are careful about mutability a la monads / uniqueness / regions /
single assignment?

it seems really frustrating to me that we all know unconstrained
mutation is evil, and yet things like Java or .Net which don't
constrain it are "ahead" in the sense of having libraries to do pretty
much any darned thing you might want.

could do some code generation to wrapper Java or .Net libraries to
somehow make them immutable? yuck, no. presumably the performance
would kind of suck vs. structures defined from the get-go from the FP
immutable-copy-on-write-persistent-shared-sub-structures approach?
and, more important, it doesn't do you any good when it comes to
offering some reassurance that the 3rd party library you downloaded
isn't junky because it just uses mutability willy-nilly; it would be
preferable if everything in the ecosystem was fundamentally based on
the proper taming of mutation. greatly reduces that aspect of code
inspection / review responsibilities.

scala is sorta offering headway with its immutable collections, i
guess, but overall the language has no guarantees or checks enforcing
proper control over mutability. it is all up to people being on their
best behaviour and not making any mistakes ever -- not an ideal
situation imho.

gracias.

p.s. unfortunately i'm not anywhere remotely programming-language-
theory enough to ever work on my own language. so i'm just nothing
more than the peanut gallery.