README.md

Monkey Lang

Overview

This is a language mostly based on the fantastic books Writing An Interpreter In Go and Writing a compiler in Go. I do this for educational purposes so I can build my own stuff from ground up later.

Installation

simply clone the repo and:

cd MonkeyLang
go build -o monkey main.go

to start the REPL (interactive mode):

./monkey

to compile and run a monkey file (*.monkey):

./monkey path/to/file

Features

the language is mostly gonna be based on the book, but shall also include more features like support for else-if expressions. Closures aren't implemented yet.

Structure

Lexer

Given an input string, we first tokenize it with the help of the Lexer. At this step we don't care about the syntax or the semantics of our language. We only define what is considered an identifier, a keyword, an operator and etc.

Parser

After tokenization, the Parser will basically check for the correctness of the syntax. It reads through the tokens and builds an Abstract Syntax Tree. The tree is an abstract summarization of our grammar for the given input. it is abstract because it does not contain some inessential parts of the syntax like punctuation(braces, brackets and etc.) It must be noted that Pratt Parsing is the author's choice for the parsing algorithm.

Eval

We give meaning to whatever we accept as valid input. This means that we need to implement some sort of object system to keep track of things. In monkey everything is an object. We even have first class functions(we can pass them around and assign them to variable . we even have closures). the Eval() function evaluates the input recursively. Environments are created as a way to keep track of identifiers and the values associated with them(kind of like scopes). Functions have their own environments that are the extension of the environment they were defined in. That is precisely the reason why closures are possible.

Compiler & Virtual Machine

This would serve as a replacement for the Eval method. The complier would emit ad hoc instructions for our vitual machine to execute. The virtual machine is aptly named, as it similuates a made-up machine and operates on our made-up instructions(Intermediate Representation). A lot of parallels can be drawn with a real world machine and architecture (ie. X86, arm, etc.) like calling convetions, jump instructions etc.