talk.md

Let's make a compiler

---

Okay, first lets talk about compilers

• software that takes code written in one language and converts it to another
• PHP -> C
• C -> Machine Code

---

Why do we need compilers

• code written for humans is hard for computers to understand
• code written for computers is hard of humans to understand

Machine Code example:

 11100101 11011001 11010010 11110001

---

Breaking a compiler down

• Front End - Takes source file and turns it into an intermediate representation
• Middle End - Makes performance optimisations
• Back End - Turns intermediate representation into the target code

---

Parts of the compiler we will look at

Front End

• Tokenizer (sometimes called a Lexer)
• Parser

Back End

• Code Generator

---

Tokenizer

Takes your code and turns it into understandable single chunks.

def hello()

becomes

token: def
token: identifier (hello)
token: open_parenthesis
token: close_parenthesis

---

Parser

Turns tokens into an Intermediate Representation

 1 + 1

becomes

token: 1
token: +
token: 1

becomes

   (+)
  /   \
(1)   (1)

---

Code Generator

Takes our Intermediate Representation and turns it into the code we care about.

   (+)
  /   \
(1)   (1)

becomes

add(1,1)

---

Sidenote: Transpilers

• just another form of compiler. It keeps code at the same level of abstraction.
• Babel es2015 stuff
• what we're going to write today

---

Demo Time!

toby.pants << 💩

---

What we've covered

• a compiler is just a program, doing normal programmy things
• the main parts of a compiler
  • Front / Middle / Back ends
  • Tokenizer
  • Parser
  • Code Generator
• the difference between a Transpiler and a Compiler
• how we could make a (very quick and dirty) compiler

---

Questions / Thanks! / Simple CS

• thanks to Destroy All Software
• slides and code https://github.com/tosbourn-ltd/compiler-talk
• @tosbourn on twitter if you want to tweet questions later
• https://tosbourn.com/simple-cs/