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I guess I need to watch some of the videos he links, because this sounds horrible to me. I mostly work in Python, which has a repl (though I'm sure not as comp

I guess I need to watch some of the videos he links, because this sounds horrible to me. I mostly work in Python, which has a repl (though I'm sure not as complete) and sometimes I poke around in it. But if I am working on a real project, or even just a small script, I always want to run it from the beginning on every invocation, because anything short of that is not proof that it works. "Editing a running system" sounds like a nightmare! How could you ever know things would actually work?!

dimovich 6y ago
I see REPL driven development more akin to writing music. I pick up the guitar and start playing. I can work on a small fragment and improve it until it sounds good to me. Or I can play the whole song. At all times I have instant feedback and I can hear what I'm working on. In the case of the REPL you are playing your program. You can play a file, a function, or half of a function. Until it sounds right. I lack the skill to use music notation for composition, so I rely on my instrument to give me feedback. And I lack the skill to execute the program in my head before I press compile, that's why I rely on the REPL.
jdminhbg 6y ago
> "Editing a running system" sounds like a nightmare! How could you ever know things would actually work?! This is why Clojure developers love immutable data and pure functions so much. Say I am writing a web frontend for managing a list of users, and I want to implement some kind of filter and grouping flow on them for some business reason. Since I know the users are immutable, I know that when I am evaluating code in the browser to test out exactly what filter logic is correct I am not actually changing anything about the system.
barrenko 6y ago
It's a really different REPL paradigm.
- quasarj 6y ago
  What is? Clojure? Can you explain?
deleted 6y ago
[deleted]
sedachv 6y ago
How do you use your computer? A Unix shell is literally a REPL over a stateful filesystem.
gradys 6y ago
It works much better when using immutable data and mostly side-effect-free functions as is heavily encouraged by Clojure.
alex_smart 6y ago
I do use REPL-driven development even for Python. (And why not? Like Norvig says, Python is basically lisp with traditional syntax.) > How could you ever know things would actually work?! Eventually you would run the project from beginning to end to make sure it works. REPL just allows you to by-pass that during development for rapid feedback. If the project takes 2-3 seconds to boot, we are talking about a difference of getting feedback in milliseconds vs several seconds - which makes a huge qualitative difference in developer workflow. The point is precisely that you do NOT have to run it from beginning on every invocation. Doing it once in a while is enough.
tmountain 6y ago
Late to the conversation, but... I think unit vs integration testing is a good model for comparison. When I'm working in a REPL, I'm trying out individual functions to ensure that they provide the desired results (unit). Most functions are referentially transparent (if not totally pure), so this allows for fast/easy experimentation. If I want to test major code paths in a program, I can call "driver functions" or primary code paths to explore the results (integration). None of this is a substitute for real unit/integration testing, but it makes for some very rapid development. I worked in a lot of "REPL" (Python included) before I had the creme de la creme experience of using Clojure with Spacemacs and Cider. It's truly a different beast, and I'd withhold judgement until you've tried it (or something very comparable).
herewulf 6y ago
I liked this video. https://vimeo.com/230220635 https://vimeo.com/230220635 I had similar preconceptions from Python's REPL. Now after reading (at the least the first section of) the article and watching the video my mind is blown. I've also been dabbling with Emacs Lisp recently and it appears that you can do basically the same thing.

dimovich 6y ago

I see REPL driven development more akin to writing music. I pick up the guitar and start playing. I can work on a small fragment and improve it until it sounds good to me. Or I can play the whole song. At all times I have instant feedback and I can hear what I'm working on. In the case of the REPL you are playing your program. You can play a file, a function, or half of a function. Until it sounds right. I lack the skill to use music notation for composition, so I rely on my instrument to give me feedback. And I lack the skill to execute the program in my head before I press compile, that's why I rely on the REPL.

jdminhbg 6y ago

> "Editing a running system" sounds like a nightmare! How could you ever know things would actually work?! This is why Clojure developers love immutable data and pure functions so much. Say I am writing a web frontend for managing a list of users, and I want to implement some kind of filter and grouping flow on them for some business reason. Since I know the users are immutable, I know that when I am evaluating code in the browser to test out exactly what filter logic is correct I am not actually changing anything about the system.

barrenko 6y ago

It's a really different REPL paradigm.

quasarj 6y ago
What is? Clojure? Can you explain?

deleted 6y ago

[deleted]

sedachv 6y ago

How do you use your computer? A Unix shell is literally a REPL over a stateful filesystem.

gradys 6y ago

It works much better when using immutable data and mostly side-effect-free functions as is heavily encouraged by Clojure.

alex_smart 6y ago

I do use REPL-driven development even for Python. (And why not? Like Norvig says, Python is basically lisp with traditional syntax.) > How could you ever know things would actually work?! Eventually you would run the project from beginning to end to make sure it works. REPL just allows you to by-pass that during development for rapid feedback. If the project takes 2-3 seconds to boot, we are talking about a difference of getting feedback in milliseconds vs several seconds - which makes a huge qualitative difference in developer workflow. The point is precisely that you do NOT have to run it from beginning on every invocation. Doing it once in a while is enough.

tmountain 6y ago

Late to the conversation, but... I think unit vs integration testing is a good model for comparison. When I'm working in a REPL, I'm trying out individual functions to ensure that they provide the desired results (unit). Most functions are referentially transparent (if not totally pure), so this allows for fast/easy experimentation. If I want to test major code paths in a program, I can call "driver functions" or primary code paths to explore the results (integration). None of this is a substitute for real unit/integration testing, but it makes for some very rapid development. I worked in a lot of "REPL" (Python included) before I had the creme de la creme experience of using Clojure with Spacemacs and Cider. It's truly a different beast, and I'd withhold judgement until you've tried it (or something very comparable).

herewulf 6y ago

I liked this video. https://vimeo.com/230220635 https://vimeo.com/230220635 I had similar preconceptions from Python's REPL. Now after reading (at the least the first section of) the article and watching the video my mind is blown. I've also been dabbling with Emacs Lisp recently and it appears that you can do basically the same thing.