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On Repl-Driven Programming

mikelevins.github.io

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Re: On Repl-Driven Programming

#161

Post by juststeve »

zmmmmm wrote: post #101

I have a concern about REPL driven development, which is around how maintainable the result is. The reason people like REPLs is because they can experiment to discover the right way to write the code in a very fast feedback loop. This alleviates a huge pain when you are operating with uncertainties or at the edge of your knowledge - 'does this function return null if no matching entries or an empty list?' - etc. The…

100%, and that also applies to the original author.

Building a script from the REPL might mean running different parts of the code out of order (such as reloading a function definition). As you mentioned, it's easy to lose track of state, writing 'clever'/unmaintainable code, and forgetting the order and purpose of the code.

Re: On Repl-Driven Programming

#162

Post by IlliOnato »

zmmmmm wrote: post #101

I have a concern about REPL driven development, which is around how maintainable the result is. The reason people like REPLs is because they can experiment to discover the right way to write the code in a very fast feedback loop. This alleviates a huge pain when you are operating with uncertainties or at the edge of your knowledge - 'does this function return null if no matching entries or an empty list?' - etc. The…

I think your concern is valid, but I think it's the general case with any powerful tool: it can be abused, or shoot you in the foot, and requires discipline to apply.

I don't have REPL-driven development experience, but I think we are all familiar with StackOverflow. This is a great, great resource, but it lead scores of programmers to the "style" of development, where they mindlessly copy solutions from SO, without understanding of how and why they work.

I guess one can extend the old maxim "there is not now, nor ever will be a programming language that makes it easier to write a good program than a bad one"...

(edited grammar)

Re: On Repl-Driven Programming

#163

Post by hchz »

FraserGreenlee wrote: post #80

I don’t see how this is different from using the pdb Python module? You can catch exceptions and use to write functions.

The biggest distinction I see is the ability to continue from exceptions.

I find the other differences to be minor in comparison - to be able to recover and continue execution following post-mortem debugging is amazing.

Re: On Repl-Driven Programming

#164

Post by heresie-dabord »

zmmmmm wrote: post #101

I have a concern about REPL driven development, which is around how maintainable the result is. The reason people like REPLs is because they can experiment to discover the right way to write the code in a very fast feedback loop. This alleviates a huge pain when you are operating with uncertainties or at the edge of your knowledge - 'does this function return null if no matching entries or an empty list?' - etc. The…

I agree with you that the immediate start-up and feedback is a great benefit to the coder. This is why I dislike complex, Rube-Goldbergian REPL systems.

There is a use-case for a throw-away interaction with a REPL. For example, how does $builtinFuncX work, or how would $data best be imported into a structure?

A REPL can also be a good initial approach to a more ambitious problem. In this case, a REPL can be good for focus and discipline.

If the second case is going to answer your concern and be constructive, it's necessary to be able to build the code for sharing and cleanly export the code for re-use.

I've had success tackling challenges using REPLs for Python and Perl [1] in both ways. But no tooling is going to solve the problem of a sloppy teammate who claims success just because "it compiles" and "it works on my box". A person who knows how to build good tooling goes further.

[1] https://github.com/viviparous/preplish

Re: On Repl-Driven Programming

#165

Post by reddit_clone »

zmmmmm wrote: post #101

I have a concern about REPL driven development, which is around how maintainable the result is. The reason people like REPLs is because they can experiment to discover the right way to write the code in a very fast feedback loop. This alleviates a huge pain when you are operating with uncertainties or at the edge of your knowledge - 'does this function return null if no matching entries or an empty list?' - etc. The…

When a certain thing is done in repl, it usually converts into a function or two in the source code. The ad-hoc testing code is converted into unit testing.

That should help with maintenance no?

One big theoretical advantage I see in repl driven development is, I can be sure that _all_ the code has been executed at one time atleast. (In a normal edit-compile-link-test language cycle, I can not be sure of that)

Re: On Repl-Driven Programming

#166

Post by xapata »

reddit_clone wrote: post #165
zmmmmm wrote: post #101

I have a concern about REPL driven development, which is around how maintainable the result is. The reason people like REPLs is because they can experiment to discover the right way to write the code in a very fast feedback loop. This alleviates a huge pain when you are operating with uncertainties or at the edge of your knowledge - 'does this function return null if no matching entries or an empty list?' - etc. The…

When a certain thing is done in repl, it usually converts into a function or two in the source code. The ad-hoc testing code is converted into unit testing. That should help with maintenance no? One big theoretical advantage I see in repl driven development is, I can be sure that _all_ the code has been executed at one time atleast. (In a normal edit-compile-link-test language cycle, I can not be sure of that)

Yep, just copy-paste a bit of REPL history for a docstring, then use `doctest` to make sure it holds. Pretty soon you'll have ~100% test coverage. Minus the error paths you didn't test in REPL.

Re: On Repl-Driven Programming

#167

Post by reddit_clone »

Buttons840 wrote: post #155
mikelevins wrote: post #154

Earlier quoted context omitted.

That rule absolutely does not work for me. For me, the whole point of the repl is that I want to build something incrementally, interactively, building it a little at a time by making small changes to it. I want it in memory, running and responding to my changes as I make them. Put this here; put that there. Change that around. Let me look at it; nope. Put that back where it was. Now add this. If the repl is stateles…

I don't mean the REPL is stateless, but the code developed using the REPL would ideally be stateless. Stateless code would be easier for others to experiment with in their own REPL, without "oh no, you broke production with your REPL!"

Right. I usually start with creating global objects in the repl. Write little snippets in the repl to operate on these. The snippets end up with all these objects parameterized as functions. Which I can test again from the repl itself.

Turn the testing code into unit test as I go along.

Rinse. Repeat.

Re: On Repl-Driven Programming

#168

Post by reddit_clone »

0x445442 wrote: post #137
jmchuster wrote: post #122

Earlier quoted context omitted.

This is what I use as my canonical example of REPL-driven development. https://vimeo.com/230220635 The main thing that stands out to me is playing with small snippets of code in real-time as you're writing it. Contrast that with writing a class and methods, then writing unit tests, then running them. There might as much as ten minutes between the time you start writing your code and when you run any portion of it, an…

Having never developed code professionally in Lisp, my question would be; does the REPL work flow replace test code? Because if the REPL is being used as a replacement for tests, then I can see future readers having a harder time groking the code without the benefit of test driver code to analyze.

Nothing is lost. You would convert the ad-hoc test code from the repl into actual unit tests in your source code. With the added good feeling they have already been executed successfully at least once.

Re: On Repl-Driven Programming

#169

Post by proverbialbunny »

xg15 wrote: post #133

Question by someone who never used interacted development before: How do you save the results of your work? How do you ensure the state of your program is what you think it is. E.g.: Imagine you're in a breakloop as described in the article. You find that local variable X is 5 when it really should be 4, so you quickly set it to 4. You find function foo() is not defined, so you define it. You continue and your progra…

It depends what kind of environment you're using. Eg, notebooks like Jupyter are a kind of REPL environment, which is how data scientists typically write code. You prototype in a cell that is the source code that gets saved. If you've finalized the function or piece you're working on, you go to another cell.

The reason data scientists do it this way is load times are gruesome for data science work. Sometimes it takes days to process something. Imagine every time you change a line of code having to wait days to see if there is a bug in code or what the output is. Instead we run it in an environment that loads it once and keeps it in ram (a REPL), so when working on code below what is already loaded there are no load times.

There are other kinds of environments though. Sometimes video game devs develop on a REPL where the game is running, they pause it, update some code, and then go back into the game with the updates automatically put in. No load times.

Re: On Repl-Driven Programming

#170

Post by petemc_ »

Folcon wrote: post #131
xkeysc0re wrote: post #124

Earlier quoted context omitted.

>What I ended up using heavily was REPL to file integration, which gave me the ability to write a function normally, evaluate it in the attached REPL session, and then play around with it in the REPL. This is far short of the “REPL driven development” that’s commonly discussed, and frankly something that’s probably possible with the Python REPL if they wanted to. I mean, yeah. You just import the Python module you're…

I'm personally of the opinion that this isn't the same thing and I'm saying this as someone who wants to do this in python. Unless you've figured it out? In which case please say, because I want to code python like this. Specifically I write code in my editor, hit a keystroke and all the code at the cursor gets sent to my running python and evaluated. The editor needs to be aware of python's indenting rules so it can…

Not a keystroke and I'm probably being captain obvious, but I use pythons execfile for this.
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