Added compilation pipeline

README.md

@@ -25,3 +25,27 @@ The project is split into several directories and submodules to ease human inspe
         - `src/util/bytecode/objects.nim` -> Contains object wrappers for bytecode opcodes
     - `src/util/debug.nim` -> Contains the debugger
 
+## Language design
+
+NimVM is a generic stack-based bytecode VM implementation, meaning that source files are compiled into an
+imaginary instruction set for which we implemented all the required operations in a virtual machine. NimVM
+uses a triple-pass compiler where the input is first tokenized, then parsed into an AST and finally optimized
+before being translated to bytecode.
+
+The compilation toolchain has been designed as follows:
+- First, the input is tokenized. This process aims to break down the source input into a sequence of easier to
+    process tokens for the next step. The lexer (or tokenizer) detects basic syntax errors like unterminated
+    string literals and multi-line comments and invalid usage of unknown tokens (for example UTF-8 runes)
+- Then, the tokens are fed into a parser. The parser recursively traverses the list of tokens coming from the lexer
+  and builds a higher-level structure called an Abstract Syntax Tree-- or AST for short-- and also catches the rest of
+  static or syntax errors such as illegal statement usage (for example return inside a function), malformed expressions
+  and declarations and much more
+- After the AST has been built, it goes trough the optimizer. As the name suggests, this step aims to perform a few optimizations,
+  namely:
+  - constant folding (meaning 1 + 2 will be replaced with 3 instead of producing 2 constant opcodes and 1 addition opcode)
+  - global name resolution. This is possible because NimVM's syntax only allows for globals to be defined in a way that
+    is statically inferrable, so "name error" exceptions can be caught before any code is even ran.
+  The optimizer also detects attempts to modify a constant's or a let's value at compile-time.
+- Once the optimizater is done, the compiler takes the AST and compiles it to bytecode for it to be later interpreted
+  by our virtual machine implementation
+