>> Embrace the REPL

2015-07-23

As some of you may be aware, the tool of my choice is vim (or neovim). Two of the languages I write a lot in are Haskell and Python, because both of these languages are very nice to quickly prototype something in. Both of these languages also feature what is known as a REPL, a Read-Eval-Print-Loop, a feature that has been around in Lisp since the fifties. The name also comes from the Lisp origin:

(loop (print (eval (read))))

Todays, arguably more modern languages have more sophisticated REPLs, like Haskell’s GHCi, Python’s IPython, BPython, etc. each coming with additional features to make testing something quickly really simple.

It just happens to be that other text-editor, [emacs][emacs], that also uses its own Lisp flavour as scripting language, also provides excellent support for Lisp REPLs in the form of SLIME. SLIME allows the user to evaluate Lisp from a emacs buffer directly in a REPL in another buffer. I have seen this functionalility at a talk recently and wanted to replicate it in vim. As it turns out, there is something called vim-slime. Because vim cannot directly handle Lisp, it uses a more general approach by using screen or tmux. It also handles things like let prefixes in Haskell, and :{/:} for multi-line pasting. There is also special support for handling the indentation levels in Python. But enough listing of features, a picture says more than a thousand words, especially if it is a gif.

vim-slime in action