• Languages have their strong applications. OCaml is known for being awesome to build PLs. but why? What’s the fuss? I’m going to show you via concrete code examples.
  • Original Rust compiler
  • Full-stack tools: Hazel, Dark
• I’ve built the MAL lisp in Ruby (see the TCO post) and now doing it in OCaml.
  • Like the TodoMVC of language implementations
• Ruby isn’t bad but it’s no OCaml for this purpose.
  • dynamic OO(ish) lang with lots of mutation
  • vs. static functional lang with mostly immutable.

Little notes:

• Link to Jon Edwards post?
• Note ReasonML is a potential for full stack envs too.
• Note the “Sweet spot”, Matt Might

Why it’s great

Static typing

• so many bugs fixed
• tagged unions
• ad hoc nil checks in ruby are covered in ocaml
• no annotations needed due to inference
  • maybe we’ll cover how this works sometime soon. OCaml is a great lang for implementing type inference.
• can be a little annoying sometimes that it’s hard to get the program to run
  • I wish there were “type warnings” as Yegge said in his compilers essay, or Typescript has.
  • tricks:
  • fill in bogus code that passes type checking
  • adding type annotations to guide type inference

Pattern matching

• tagged unions + destructuring, amazing
• show some examples of where pattern matching rules
• exhaustiveness checking catches weird cases

Immutable (mostly)

• contrast environment mutation
• note how ref makes it easy to still manage limited mutable state
• reasoning about env state in ruby isn’t as easy

Why it’s not

• ugh, tooling (link to Paul Biggar’s post)
• Makefile, library linking, etc
• some exciting news on this front from the OCaml platform keynote