add melange 4.0 announcement blogpost (#182)

* add melange 4.0 announcement blogpost

* address feedback

blog/posts/melange-4-is-here.md

@@ -0,0 +1,105 @@
+---
+title: Melange 4.0 is here
+date: 2024-05-22
+author: Antonio Monteiro
+gravatar: 45c2052f50f561b9dc2cae59c777aecd794f57269fa317f9c9c3365c2e00d16f
+twitter: '@_anmonteiro'
+---
+
+Today, we're introducing Melange 4.0, the latest version of our backend for the
+OCaml compiler that emits JavaScript.
+
+Melange is now compatible with OCaml 5.2! In this release, Melange starts
+emitting more ES6 constructs, supports more JavaScript builtins, improves error
+handling, and makes using Dune virtual libraries fully supported. Read on for
+more details.
+
+---
+
+## Embracing OCaml 5.2
+
+OCaml 5.2 was released just last week. With Melange 4, you can now leverage all
+the power and enhancements in this latest OCaml version. We've upgraded the
+OCaml type checker and the standard library to match OCaml 5.2's, ensuring you
+can select a 5.2-compatible Melange in your projects.
+
+This does **not** mean Melange is only compatible with OCaml 5.2. As previously
+mentioned in the [Melange 3
+announcement](./announcing-melange-3#multiple-ocaml-version-releases), each
+Melange version ships one release for every compiler version that it supports;
+for OCaml 5.1, this would correspond to Melange `4.0.0-51`.
+
+## Full Support for Dune Virtual Libraries
+
+Melange now fully supports [Dune virtual
+libraries](https://dune.readthedocs.io/en/stable/variants.html), which requires
+Dune 3.15.2. There were a few bumps in road when we thought it wouldn't be
+possible to support this use case in Melange. We were thankfully proven wrong
+([#1067](https://github.com/melange-re/melange/pull/1067)), and we think that
+virtual libraries can become an interesting way to write libraries that work
+across Melange and native OCaml, sharing a common interface.
+
+## Emitting ES6 and Enhanced JavaScript Interop
+
+In this release, Melange starts emitting ES6, particularly:
+
+- Melange 4.0 emits `let` instead of `var`, and `const` where possible
+  ([#1019](https://github.com/melange-re/melange/pull/1019),
+  [#1059](https://github.com/melange-re/melange/pull/1059)).
+- Emitting `let` allowed us to remove a bit of legacy code related to compiling
+  `for` loops, taking advantage of `let`'s lexical scoping.
+  ([#1020](https://github.com/melange-re/melange/pull/1020))
+
+In our effort to expand the API surface area for JavaScript interoperability,
+we've added new bindings to a few more JavaScript features in the `melange.js`
+library (whose main entrypoint is the `Js` module):
+
+- **Js.Bigint**: [#1044](https://github.com/melange-re/melange/pull/1044) added
+  bindings to work with `BigInt`;
+- The **Js.Set** and **Js.Map** modules now bind to even more methods available
+  in these JavaScript data structures
+  ([#1047](https://github.com/melange-re/melange/pull/1047),
+  [#1101](https://github.com/melange-re/melange/pull/1101)).
+- **JS Iterators**: We introduced minimal bindings for JavaScript iterators,
+  making it easier to work with iterable objects, which some other modules'
+  methods can now return
+  ([#1060](https://github.com/melange-re/melange/pull/1060)).
+- **WeakMap and WeakSet**: Bindings for these weakly referenced collections
+  have also been added
+  ([#1058](https://github.com/melange-re/melange/pull/1058)).
+
+## Improved Error Handling and Code Generation
+
+In this release, we've also made significant improvements in how Melange
+handles errors and generates JavaScript code:
+
+- Instead of throwing JavaScript objects with Melange exception payloads, we
+  now emit a Melange-specific error (`throw new MelangeError(..)`) for more
+  consistent error handling
+  ([#1036](https://github.com/melange-re/melange/pull/1036)).
+  - An interesting corollary to this change is that catching Melange errors
+    from external JavaScript only needs to check `instanceof MelangeError`.
+
+## Additional Fixes & Enhancements
+
+- **Slimmer Executable**: We've removed unnecessary internal code from
+  `melange-compiler-libs`, making the Melange compiled executable smaller in
+  size and faster to build
+  ([#1075](https://github.com/melange-re/melange/pull/1075)).
+- **Float Operations**: Fixed runtime primitives for `Float.{min,max}` and
+  related functions, ensuring more accurate mathematical operations
+  ([#1050](https://github.com/melange-re/melange/pull/1050)).
+- **Warning 51 (`wrong-tailcall-expectation`)**: Melange 4 ships with support
+  for enabling warning 51 and triggering the warning when
+  [`[@tailcall]`](https://ocaml.org/manual/5.2/attributes.html#ss:builtin-attributes)
+  is used ([#1075](https://github.com/melange-re/melange/pull/1075)).
+
+## Conclusion
+
+The [Melange 4.0
+changelog](https://github.com/melange-re/melange/blob/main/Changes.md#400-2024-05-15)
+lists all the changes that made it to this release.
+
+Thanks for reading and stay tuned for more updates. Happy hacking!
+
+

flake.nix

@@ -36,6 +36,7 @@
             buildInputs = with python3Packages; [
               mkdocs
               mkdocs-print-site-plugin
+              pkgs.yarn
             ];
           };
         };