Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

What makes a good REPL?

vvvvalvalval.github.io

Post reply on HN
Print view View original

71–80 of 177 posts

Re: What makes a good REPL?

#71

Post by pjmlp »

abhirag wrote: post #63
pjmlp wrote: post #58

Earlier quoted context omitted.

Emacs suffers from not being like Lisp machines REPL, meaning lacking graphical display on buffers. If I remember correctly, XEmacs used to support it (which was my favorite fork), but it seems to have faded away. For example, try to achieve this demo on Emacs. https://www.youtube.com/watch?v=o4-YnLpLgtk

I have never used a Lisp Machine so forgive my naivety but I saw the demo and you seem to be referring to the ability of displaying images inline in a buffer. Emacs can definitely do that, I have used Emacs IPython Notebook[1] which is a REPL supporting this. I could fire up a jupyter notebook and use pillow[2] to recreate the image manipulation part of the demo. [1] -- ( https://github.com/millejoh/emacs-ipython-not…

That is partially what I was referring to.

The other part, which might not be visible on that video is the integration of debugger into the REPL, and the ability to redo a piece of code after breaking into the debugger and fixing it.

So you can do something like, REPL => error (ask to start debugger) => track down and fix error => restart error expression => finish the execution of the original REPL expression with the respective result.

Re: What makes a good REPL?

#72

Post by ben-schaaf »

photojosh wrote: post #51

"Finally, not all programs need be fully automated - sometimes the middle ground between manual and automated is exactly what you want. For instance, a REPL is a great environment to run ad hoc queries to your database, or perform ad hoc data analysis, while leveraging all of the automated code you have already written for your project" This is exactly why I love Python. My Django webapp gets features (DB reports, ex…

I follow a similar procedure for an open source community project in Ruby on Rails. There are a fair amount of rare things that need to get done where it's just easier to do them in a reply on the web server. One of the admins of the community actually learnt enough about the rails DSL to write basic queries through the reply and do some of the things I usually would.

Re: What makes a good REPL?

#73

Post by onikolas »

I personally prefer to develop by writing small functions and pairing them with a small test. Hacking in a REPL environment, saving the result and calling it source code has not worked out well for me, I end up producing spaghetti :)

I do however find REPL to be invaluable when experimenting/doing research. When you don't even know what the end result is, or when exploring data, you need to iterate over many ideas as quickly as possible and REPL is the fastest way to do that.

Re: What makes a good REPL?

#74

Post by narrowtux »

lispm wrote: post #37
christophilus wrote: post #30

I think REPLs work better in languages that provide 1st class immutability support, since it's easier to set up state once, then play with functions without having to re-set up state every time you tinker.

I think REPLs work better in languages that don't provide 1st class immutability support, since it's easier to change state, then play with functions without having to re-set up state every time you tinker.

You could just store your modified state to new variables though

Re: What makes a good REPL?

#75

Post by mjmein »

agentgt wrote: post #47

With fast compiling languages a unit test is not for off from being a REPL. In Java I use JUnit as a REPL. Actually I prefer unit tests over a REPL the same reason I prefer bash scripts over one liners or SQL scripts instead of typing into the interpreter... I don't like the ephemeral nature of REPLs. Also with true REPLs unlike the debug unit test approach I mention with Java you really need the language to be dynam…

The thing to realise is that, at least is my experience, REPL based development doesn't mean your are actually typing code into the REPL.

Instead, you develop code in a file, but constantly evaluate code as you go along.

When I work on a clojure project, I very rarely open the actual REPL, but I am constantly evaluating code and experimenting with different implementations of functions.

Then, when I'm happy with the results, I ask the editor to evaluate and insert the results back into the editor. This then becomes the unit test.

Re: What makes a good REPL?

#76

Post by lispm »

tedmiston wrote: post #61
agentgt wrote: post #47

With fast compiling languages a unit test is not for off from being a REPL. In Java I use JUnit as a REPL. Actually I prefer unit tests over a REPL the same reason I prefer bash scripts over one liners or SQL scripts instead of typing into the interpreter... I don't like the ephemeral nature of REPLs. Also with true REPLs unlike the debug unit test approach I mention with Java you really need the language to be dynam…

One nice thing about the Python REPL IPython is the ability to turn the ephemeral session into a file which contains every command in the session like a history file by just typing %logstart. Most of my projects start this way.

Lisp has the function DRIBBLE for that.

SLIME provides slime-repl-save-history ...

Re: What makes a good REPL?

#77

Post by junke »

Vendan wrote: post #45
lispm wrote: post #35

Earlier quoted context omitted.

A 'command line interface', for example for bash, does the same. What is the difference to a REPL? Is it just another name for the same concept or are there differences? What do you think?

Yes, it's technically a REPL, just as bash is a scripting language.

It is a subtyping relationship. Bash's command line is a (minimalistic) REPL, but not all REPL are like Bash's command line. In most contexts, talking about REPLs is implicitly talking about REPLs that do more than just read, eval and print, however illogical that may sound.

Note that few languages actually define READ in a user-friendly way (since python 2.6 you have the ast package, Bash's "read" returns strings).

Re: What makes a good REPL?

#78

Post by yorwba »

junke wrote: post #67
yorwba wrote: post #65

Earlier quoted context omitted.

I think Jupyter has the right idea here with various kinds of repr -alternatives that can render html or images directly into the notebook. http://ipython.readthedocs.io/en/stable/config/integrating.h...

This is the kind of use cases where multiple dispatch is useful.

How so? I feel like single dispatch (as in Python) is already enough.

Re: What makes a good REPL?

#79

Post by abhirag »

pjmlp wrote: post #71
abhirag wrote: post #63

Earlier quoted context omitted.

I have never used a Lisp Machine so forgive my naivety but I saw the demo and you seem to be referring to the ability of displaying images inline in a buffer. Emacs can definitely do that, I have used Emacs IPython Notebook[1] which is a REPL supporting this. I could fire up a jupyter notebook and use pillow[2] to recreate the image manipulation part of the demo. [1] -- ( https://github.com/millejoh/emacs-ipython-not…

That is partially what I was referring to. The other part, which might not be visible on that video is the integration of debugger into the REPL, and the ability to redo a piece of code after breaking into the debugger and fixing it. So you can do something like, REPL => error (ask to start debugger) => track down and fix error => restart error expression => finish the execution of the original REPL expression with t…

The only debugging experience I find enjoyable in Emacs is debugging Clojure using cider[1] and I think it comes close to what you are describing but I think you might already be aware of that :)

[1] -- (https://github.com/clojure-emacs/cider/blob/master/doc/debug...)

Re: What makes a good REPL?

#80

Post by yorwba »

narrowtux wrote: post #74
lispm wrote: post #37

Earlier quoted context omitted.

I think REPLs work better in languages that don't provide 1st class immutability support, since it's easier to change state, then play with functions without having to re-set up state every time you tinker.

You could just store your modified state to new variables though

Or you could just make copies of state you want to keep before mutating it. Both mutable imperative code and immutable functional code can emulate each other, so which one to choose largely depends on your preferences.
Post reply on HN