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Posts   tagged   “lisp”

Here are some of my latest thoughts on lisp… such as thread-first and loop (•̀ᴗ•́)و

💐 Repl Driven Development: /Editor Integrated REPLs for all languages/ 🔁

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The MELPA package makes the philosophy of REPL Driven Development (RDD) accessible to any language that has a primitive CLI repl: The result is an Emacs interface for the language, where code of your choosing is evaluated, and results are echoed at your cursor in overlays.

That is, with Repl aided development, you make software by starting with an already working program (i.e., the repl) then incrementlly “teach it” to be the program you want, by defining & redefining things. Until satisfied, loop: Type/modify code in your editor, press some keys to evaluate what you wrote/modified in the currently running system, and explore/test the resulting runtime.

RDD is programming emphasising fast & rich feedback from a running system. RDD is fantastic for quickly teaching/exploring an idea; as such, the running example of this article will be on servers —no prior experience with servers is assumed. The main examples will be in JavaScript, Python, and Java. (Since JavaScript is just Lisp in C clothing, we will not discuss Lisp.) Since Java is verbose, the power of REPLs really pays off when exploring a new idea. We see how many imports and setup-code simply disappear in the RDD approach, letting you focus on the core idea you're exploring/teaching. For comparison, a traditional self-contained Java server program is ~30 lines long whereas the focused RDD approach is ~4 lines long.

tdlr: This library provides the Emacs built-in C-x C-e behaviour for arbitrary languages, provided they have a primitive cli REPL.

💐 Making VSCode itself a Java REPL 🔁

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VSCode evaluates Java code wherever it sees it, by sending it to a JShell in the background, and echos the results in a friendly way!

This is achieved with a meta-extension for VSCode that makes VSCode into a living, breathing, JS interpreter: It can execute arbitrary JS that alters VSCode on-the-fly. (Inspired by using Emacs and Lisp!)

The relevant docs show how to make a similar REPL for Python, Ruby, Clojure, Common Lisp, JavaScript, Typescript, Haskell, and of-course Java.

Typed Lisp, A Primer

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Let's explore Lisp's fine-grained type hierarchy!

We begin with a shallow comparison to Haskell, a rapid tour of type theory, try in vain to defend dynamic approaches, give a somewhat humorous account of history, note that you've been bamboozled —type's have always been there—, then go into technical details of some Lisp types, and finally conclude by showing how macros permit typing.

Goals for this article:

  1. Multiple examples of type constructions in Lisp.
  2. Comparing Lisp type systems with modern languages, such as Haskell.
  3. Show how algebraic polymorphic types like Pair and Maybe can be defined in Lisp. Including heterogeneously typed lists!
  4. Convey a passion for an elegant language.
  5. Augment Lisp with functional Haskell-like type declarations ;-)

Unless suggested otherwise, the phrase “Lisp” refers to Common Lisp as supported by Emacs Lisp. As such, the resulting discussion is applicable to a number of Lisp dialects —I'm ignoring editing types such as buffers and keymaps, for now.

Thanks for reading everything! 😁 Bye! 👋

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Life & Computing Science by Musa Al-hassy is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License