Improve README

Author: DQNEO

README.md

@@ -1,28 +1,84 @@
-# Babygo: a go compiler made from scratch
+# Babygo, a go compiler made from scratch
+Babygo is a small and simple go compiler. (Smallest and simplest in the world, I believe.)
+It is made from scratch and can compile itself.
 
+* No dependency to any libraries. Standard libraries and calling of system calls are home made.
+* Lexer, parser and code generator are hand written.
+* Emit assemble code which resutls in a single static binary.
 
-# Target machine
+It depends only on `as` as an assembler and `ld` as a linker.
 
-x86-64 Linux
+It is composed of only 3 files.
 
-# Test
+* main.go - the main compiler
+* runtime.go - runtime and standard library
+* runtime.s - low level of runtime
 
-```terminal
+# Design
+
+## Lexer, Parser and AST
+The design and logic of ast, lexer and parser are borrowed (or should I say "stolen")  from `go/ast`, `go/scanner` and `go/parser`.
+
+## Code generator
+The design of code generator is borrowed from [chibicc](https://github.com/rui314/chibicc) , a C compiler.
+
+## Remaining parts (Semantic analysis, Type management etc.)
+This is purely my design :)
+
+# Environment
+
+It supports x86-64 Linux only.
+
+If you are not using Linux, you can use [a dedicated docker image](https://hub.docker.com/r/dqneo/ubuntu-build-essential/tags) for this project.
+
+```termiinal
+$ docker pull dqneo/ubuntu-build-essential:go
 $ ./docker-run
-# make test
 ```
 
-# How to do self hosting
+# Usage
+
+## Hello world
 
 ```terminal
-$ ./docker-run
+# Build babygo
+$ go build -o babygo main.go
+
+
+# Build the hello world program by babygo
+$ ./babygo < t/hello.go > /tmp/hello.s
+$ as -o hello.o /tmp/hello.s runtime.s
+$ ld -o hello hello.o
 
-#  go build -o babygo main.go # 1st generation compiler
-# ./babygo < main.go > /tmp/babygo2.s
-# as -o babygo2.o /tmp/babygo2.s runtime.s
-# ld -o babygo2 babygo2.o # 2nd generation compiler
-# ./babygo2 < main.go > /tmp/babygo3.s
-# diff /tmp/babygo2.s /tmp/babygo3.s # assert babygo2.s and babygo3.s are same.
+# You can confirm it's a single static binary
+$ ldd ./hello
+        not a dynamic executable
+
+# Run hello world
+$ ./hello
+hello world!
+```
+
+## How to do self hosting
+
+```terminal
+# Build babygo (1st generation)
+$ go build -o babygo main.go
+
+# Build babygo by babygo (2nd generation)
+$ ./babygo < main.go > /tmp/babygo2.s
+$ as -o babygo2.o /tmp/babygo2.s runtime.s
+$ ld -o babygo2 babygo2.o # 2nd generation compiler
+$ ./babygo2 < main.go > /tmp/babygo3.s
+
+# Assert babygo2.s and babygo3.s are exactly same
+$ diff /tmp/babygo2.s /tmp/babygo3.s
+```
+
+## Test
+
+```terminal
+$ make test
 ```
 
 # LICENSE
@@ -31,4 +87,4 @@ MIT
 
 # AUTHOR
 
-@DQNEO
+[@DQNEO](https://twitter.com/DQNEO)

t/hello.go

@@ -0,0 +1,8 @@
+package main
+
+import "syscall"
+
+func main() {
+	var msg = []uint8("hello world!\n")
+	syscall.Write(1, msg)
+}