> Can you give an example of bonkers-ness?

Maybe :-)---this was a year and a half ago, or more. I do remember spending a fair amount of time trying to wrap my head around the implications of the difference between `f[x] = x^2` and `f[x_] = x^2`, and the differences between "Module", "Block", and "With". I also had a hard time with closures & symbols---I was trying use something not unlike the bank-account example from SICP (https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-20.htm...) to cache some intermediate computations, and it got very messy very quickly.

Now I recognize that this is in no way idiomatic Mathematica code, and I'm sure there is a nice Mathematica-y way to achieve this, but that's sort of my point. I have a problem, think "Aha! I know exactly how to deal with this in Scheme!", try to translate the Scheme solution into Mathematica, and either fail miserably or spend way too much time trying to figure out how to persuade Mathematica to do what I want. (I should perhaps admit that when I hear "Lisp" I think Scheme and to a certain extent CL, with lexical scoping, as opposed to elisp, with dynamic scoping. This is a flaw in my thinking I've never really gotten around to rectifying.)

> The functional parts of Mathematica/WL (by which I mean the equivalents of fold, filter, map, etc) are pretty straightforward and should be quite easy for a Lisp programmer to pick up. See [0].

Yeah, those were pretty natural.

> Note to self: clearly we aren't making it easy enough to understand what WL can do, especially for people who pick it up for one specific thing.

This is important, I think, but I also think the problem's less in your documentation than in how I "learned" Mathematica. I got started using Mathematica for things like messy integrals, or differentiating and then simplifying some huge expression. Something comes up in a problem set, I try three or four times to do it by hand and always lose signs/factors/whatever, and then farm it out to Mathematica; as I gradually started doing more and more, I kept just porting Lisp experience, and this always worked just barely well enough that I wasn't forced to learn Mathematica on its own terms.

I suspect if I had thought about it as "basically m4 with a crazy-awesome standard library", rather than "basically Scheme with a crazy-awesome standard library", I might have been happier, but ultimately I needed (need) to recognize that Mathematica is its own thing, with its own strengths, weaknesses, and fundamental metaphors.

> Btw, its called a "term rewriting system", not a "rule rewriting engine".

Ack. Thanks; I'll try to bear that in mind.

> Did you really want to write diagonalization from scratch? Why not use the superfunction Eigensystem [2], which has been honed by many experts over many years?

No! You're right, that would be a terrible idea. I was using Eigensystem; in Julia I farmed it out to LAPACK via eigs(). My problem was in setting up the matrix to be diagonalized. The state space had something like seven degrees of freedom (four two-dimensional and three with arbitrary dimensions), so I was calculating matrix elements for up to something like N = 10^5 basis states. (There were some tricks to pull so I was iterating through O(N) states, not O(N^2).)

Ultimately, for sufficiently large N, the diagonalization is going to take much longer than the setup, just because the scaling's worse. For small-ish N, though, the setup was interminable, and those small-N test cases are precisely where I need to be able to move quickly when I'm trying to figure out which stupidity I perpetrated this time.

> It's a bit odd to criticize a functional programming language for not having super-fast 'for' loops.

Yeah, no kidding. This was a classic Fortran-style problem, which is why I feel kind of stupid for having even tried to do it in Mathematica.

>> The lesson I learned, though, was to never use Mathematica for anything beyond basic symbolic calculations---integrals, that sort of thing.

>That's basically nonsense. Wolfram|Alpha is a multi-million line Mathematica/WL system that goes far beyond symbolic manipulation. As a totally random example, take Facebook social network analysis [3].

Fair enough. And I have a very smart friend who has sworn by Mathematica for years (and just spent some time working for you guys)---maybe it really is a combination of how I approach Mathematica, the types of problems I've tried to solve in it, and the fact that de gustibus non disputandum. I can't shake the feeling, though, that I'd want to run away very quickly from a large Mathematica/WL project like Wolfram|Alpha.

Edit: missing newline, missing )