We Lost Something: 1970s REPLs Were Better Than Modern Development Environments

I use a modern Lisp everyday...Clojure. My dev environment is VS Code using the most excellent Calva extension which give me REPL-everywhere in my editing experience.

Yes, that 70's experience was better...and it's still here, refined and built on modern tooling and runtimes.

I make a ton of progress with ipython and vim/st3/other text editor with a vertical split. I sometimes screen the terminal in two if I want to run external elements.

We seem to keep iterating back to that modality, but honestly, it's just nice. VS Code starts there but then Java language servers and broken Python language servers and rust language servers and exploding npm dependencies and supply chain attacks just muck everything up.

Simple simple simple is so refreshing.

I think there are benefits of interpreters as well as compilers, possibly for the same programming language in some cases (although some programming languages are better for use with interpreter and some are better for use with compilers).

I think JSON is not the best format for the persistence though (despite their claim that it is better than binary formats, it has many problems); it has many problems, such as not a proper integer type and not non-Unicode text types or binary types, etc; and different format would better, such as DER. If you use DER, then you can use better types, better character sets, binary data, and not limits to how big numbers can be, etc. (JSON might work for JavaScript, but even then only for some types; JavaScript has more types than JSON has, including JavaScript does actually have a integer type even though JSON does not.) (With using JSON, it will just mean that you will then have to wrap other data in JSON anyways (e.g. encoding DER as base64) and the meaning will have to be converted.) (Also, you can work around not being a text format, because you can have a program to display them, like a program can be used to display any other kind of data in other ways (e.g. syntax highlighting, pictures, auto formatting, etc).)

What he's getting at is single level storage. Ram isn't used for loading data & working on it. Ram is cache. The size of your disk defines the "size" of your system.

This existed in Lisp and Smalltalk systems. Since there's no disk/running program split you don't have to serialize your data. You just pass around Lisp sexprs or Smalltalk code/ASTs. No more sucking your data from Postgres over a straw, or between microservices, or ...

These systems are magnitudes smaller and simpler than what we've built today. I'd love to see them exist again.

No love for Forth? The opening paragraph just nails the whole concept of a machine operator instead of machine programmer - the driving principle behind Forth, right?

> true interactive, exploratory programming environments where developer feedback was instantaneous, context was persistent, and the entire system was designed around the developer’s cognitive workflow.

Reminds me of smalltalk? I’ve played a bit with Pharo and it seems to tick all those boxes

My favorite debugging method is still printf()

Are there any current language REPLs that have save/restore session state commands?

This is just my 2 cents.

This is why I programmed in Pharo (a Smalltalk descendant) professionally for a while to get that experience [1].

I feel like that using iPython is good enough of an experience to be honest. Could it be better? Sure.

But the fact that this is my iPython session:

ipython Python 3.12.9 | packaged by conda-forge | (main, Mar 4 2025, 22:44:42) [Clang 18.1.8 ] Type 'copyright', 'credits' or 'license' for more information IPython 8.32.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: def foo(): ...: return 'bar' ...:

In [2]: foo() Out[2]: 'bar'

In [3]: def foo(): ...: return 'baz' ...:

In [4]: foo() Out[4]: 'baz'

says a whole lot I think :)

The cool thing with Pharo and Lisp of course is the whole "treating code as data", where Lisp is arguably even more intense at it than Pharo - since the syntax is basically an abstract syntax tree. It really allows for automated reasoning (e.g. "give me all functions of xyz type with abc parameters, constrained to only pqr classes and only showcase the lines where they were being called, skip the definitions). So that's awesome. I haven't tested Python on this a whole lot yet and I don't know enough about Lisp to say anything useful about it, but with Pharo I vaguely remember doing some insane things since you can also access the AST and have reflection on that as well.

Pharo of course has the whole debugger inside a debugger inside a debugger experience. But that has had quite some limited use because a new process is spawned for that new debugger, so you won't have access to the exact same context that you need. I vaguely remember that some class based variables didn't have the state I needed when I went debugger inside a debugger mode. I think it was WADynamicVariable of the Seaside framework and it was because it was a singleton like thing (IIRC) and in order to have a certain behavior it could only do that by triggering exceptions (I really don't remember it well). The point is, it needed such obscure behavior to behave in the way it needed to that the debugger inside a debugger wasn't expected to copy that exception flow context, as it wasn't really intended to be used like that.

[1] I would've worked there for longer but the company got Americanized. Our company - that was profitable - got subsumed by a venture capitalist firm that had 2 companies like it that were unprofitable. We became a subsidiary/sub-company basically. Suddenly tech layoffs came, 2 rounds at least, because the company as a whole was unprofitable (as in: the other 2 subsidiaries were unprofitable and we had to pay the price). I'd have stayed there for much longer if that didn't happen. I will go on record and say that: it is my personal opinion that they destroyed a good company with good people. I won't name the company, but given that I'm posting under my real name, it's not too hard to figure out.

But we have the same 1970s REPLs in 2025; additionally, the web browser, how end-users consume most programs, is a giant REPL.

For interpreted languages, most fancy IDEs provide a language interpreter shell, which is a REPL.

Speaking of better in the old days, MSVC in the 90s had edit and continue, where you could stop in a debugger, change the source code and move the current breakpoint back and run it again. Even VBA had this 30 years ago, why cant I do in Python?

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