[judk]

I am worried that Sage will get stuck in the mud as its Python code base grows, without a powerful expressive functional core like Mathematica's Lisp-ish core language. For example, see the discussion in this page about simple association lists vs what Mathematica 10 just launched

[reikonomusha]

Have you noticed that in Mathematica you're not even able to make your own opaque data types? Only Wolfram has that ability.

Python is usable for actually writing software systems and algorithms. When a Mathematica code base grows over 10 lines, it becomes virtually unmaintainable in my experience.

[taliesinb]

You can make your own opaque data objects, quite easily, thanks to HoldAll, UpValues, and Internal`SetNoEntry (the nuclear option).

What precisely becomes unmaintainable about Mathematica/Wolfram Language code after 10 lines? You could just be bad at programming in WL.

[reikonomusha]

Name[Field1, Field2, ...] is not an opaque data type. Maybe you can give me an idiomatic example of how to build a binary tree, for example? Or maybe something more complicated like a doubly linked list?

I do not write Mathematica code, but most code I've seen usually ends up being this mess of functions. I'll give you that maybe the code I've seen has just been bad, so we can ignore my point there.