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title = "Overview — Compiler In A Day"
next = "01-ciadlang.md"
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# Compiler In A Day

This is intended to be a walkthrough of a complete compiler for a simple language that can be read and understood in a single day.

In order to achieve this, we're going to be cutting a lot of corners, mostly around code generation.
The assembly we'll be producing will run correctly, but it will be very inefficient.

Our compiler will accept a file written in our programming language and output x86_64 assembly, which can be assembled and linked by [GNU Binutils], intended to be run on Linux.

It should also run on the [Windows Subsystem for Linux] or on FreeBSD with its [Linux ABI support].

We'll also have a small runtime, written in C, and using [the Boehm-Demers-Weiser garbage collector].

The source code we'll show for the compiler is in Ruby, but nothing Ruby-specific will be used.
In fact, a previous version of this compiler was written in C11.

Our compiler will have four parts.
They are, in the order they get run:

- [Lexing][Lexical analysis]: the process of breaking up the strings of source code into lexical units known as "tokens." This simplifies parsing.
- [Parsing]: the process of building a tree representing the program from the tokens.
- Frame layout: the process of assigning slots in each function's [stack frame] to its local variables.
- Code generation: the process of generating actual assembly code from the program.

TODO: pictures!

Before we can start looking at these steps, however, we should look at the language we'll be compiling.

[GNU Binutils]: https://www.gnu.org/software/binutils/
[Lexical analysis]: https://en.wikipedia.org/wiki/Lexical_analysis
[Linux ABI support]: https://man.freebsd.org/cgi/man.cgi?query=linux&sektion=4&format=html
[Parsing]: https://en.wikipedia.org/wiki/Parsing
[stack frame]: https://en.wikipedia.org/wiki/Call_stack#Structure
[the Boehm-Demers-Weiser garbage collector]: https://en.wikipedia.org/wiki/Boehm_garbage_collector
[Windows Subsystem for Linux]: https://learn.microsoft.com/en-us/windows/wsl/