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README.md
NimVM
A basic programming language written in Nim
Project structure
The project is split into several directories and submodules:
build.py
-> The build script (TODO, not pushed yet)docs
-> Contains markdown files with the various specifications for NimVM (bytecode, grammar, etc)src
-> Contains source files
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 outside 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:
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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.
-
throw warnings for things like unreachable code after return statements (optional).
The optimization step is entirely optional and enabled by default
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- 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