Add a post about the first real program in Valeri

content/pages/projects/note.md

@@ -4,7 +4,7 @@ Open-source tools and projects: [git.sr.ht/~knazarov](https://git.sr.ht/~knazaro
 
 Highlights:
 
-* [My own programming language with a VM and garbage collector](https://git.sr.ht/~knazarov/lisp.experimental) (work in progress)
+* [My own programming language with a VM and garbage collector](https://git.sr.ht/~knazarov/valeri) (work in progress)
 * [A swiss-army script for planning team's work on GitHub](https://git.sr.ht/~knazarov/git-plan)
 * [Homebrew tap for qemu with support for 3d accelerated guests](https://github.com/knazarov/homebrew-qemu-virgl)
 * [Plain-text note taking system](https://git.sr.ht/~knazarov/notes.sh)

content/posts/first_real_program_compiled_with_valeri/note.md

@@ -0,0 +1,50 @@
+X-Date: 2024-08-23T23:49:16Z
+X-Note-Id: 175bdac4-8655-4b75-8205-f44b7311daa0
+Subject: First real program compiled with Valeri
+X-Slug: first_real_program_compiled_with_valeri
+
+I've reached my first significant milestone with [Valeri](https://git.sr.ht/~knazarov/valeri).
+It can now compile something useful to bytecode and then execute it in the virtual machine.
+
+As an example, I've implemented a simple recursive factorial function:
+
+```
+(fn fact (n)
+    (if (<= n 0)
+        1
+        (* n (fact (- n 1)))))
+
+(fact 12)
+```
+
+If you save this code as `factorial.vli`, you can then run it with `./vli factorial.vli`,
+and it will give you `479001600`, as you would expect.
+
+This may not seem impressive at a first glance, but to compile this example the compiler has to support:
+
+- modules (at least top-level)
+- functions
+- recursion
+- lexical scope
+- globals
+- constants
+- arithmetic
+
+Most importantly, this is not a recursive AST evaluator like how many people implement their first Lisp.
+This in fact compiles into a bytecode which is then executed on a virtual machine. It means that the performance
+is bad (due to lack of optimizations), but not completely abysmal.
+
+The process of compilation is now 2-step:
+
+- Read the source code into "AST" (actually the S-expression form that is a list)
+- Recursively step through the AST and emit the bytecode for known special forms
+  - As we walk the tree, keep a linked list of lexical context (to find variable bindings)
+
+To emit the bytecode, I'm following an approach that is close in spirit to the
+[Incremental Approach to Compiler Construction paper](http://scheme2006.cs.uchicago.edu/11-ghuloum.pdf).
+With the exception that the paper uses stack and an accumulator register, and my implementation is
+register-based like Lua, see [Lua 5.0 paper](https://www.lua.org/doc/jucs05.pdf) for reference.
+
+I'm very happy about the progress, but also am mindful of the fact that this is only the beginning.
+For this compiler to be really useful, it should give decent error reporting (both during the compilation
+phase and runtime phase). And this is where the real struggle will begin.