Hello, world!

What is a Compiler?

A function that maps an input string to an output string.

compiler :: String -> String

Typically, the input and output strings are “programs”

compiler :: SourceProgram -> TargetProgram

For example, here are some well-known compilers

gcc, clang :: C          -> Binary          -- a.out, .exe
ghc        :: Haskell    -> Binary                 
javac      :: Java       -> JvmByteCode     -- .class
scalac     :: Scala      -> JvmByteCode      
ocamlc     :: Ocaml      -> OcamlByteCode   -- .cmo
ocamlopt   :: Ocaml      -> Binary               
gwt        :: Java       -> JavaScript      -- .js
v8         :: JavaScript -> Binary
nasm       :: X86        -> Binary    
pdftex     :: LaTeX      -> PDF
pandoc     :: Markdown   -> PDF | Html | Doc  

Key Requirements on output program:

1. Has the same meaning (“semantics”) as input,
2. Is executable in relevant context (VM, microprocessor, web browser).

A Bit of History

Compilers were invented to avoid writing machine code by hand

Richard Hamming – The Art of Doing Science and Engineering, p25:

In the beginning we programmed in absolute binary… Finally, a Symbolic Assembly Program was devised – after more years than you are apt to believe during which most programmers continued their heroic absolute binary programming. At the time [the assembler] first appeared I would guess about 1% of the older programmers were interested in it – using [assembly] was “sissy stuff”, and a real programmer would not stoop to wasting machine capacity to do the assembly.

John A.N. Lee, Dept of Computer Science, Virginia Polytechnical Institute

One of von Neumann’s students at Princeton recalled that graduate students were being used to hand assemble programs into binary for their early machine. This student took time out to build an assembler, but when von Neumann found out about it he was very angry, saying that it was a waste of a valuable scientific computing instrument to use it to do clerical work.

What does a Compiler look like?

An input source program is converted to an executable binary in many stages:

• Parsed into a data structure called an Abstract Syntax Tree
• Checked to make sure code is well-formed (and well-typed)
• Simplified into some convenient Intermediate Representation
• Optimized into (equivalent) but faster program
• Generated into assembly x86
• Linked against a run-time (usually written in C)

What is CSE 131 ?

• A bridge between two worlds

  • High-level: ML (CSE 130)
  • Machine Code: X86/ARM (CSE 30)

A sequel to both those classes.

• How to write a compiler for NanoML -> X86

  1. Parsing
  2. Checking & Validation
  3. Simplification & Normalizing
  4. Optimization
  5. Code Generation

• But also, how to write complex programs

  1. Design
  2. Implement
  3. Test
  4. Iterate

How write a Compiler?

General recipe, applies to any large system

• gradually, one feature at a time!

We will

• Step 1 Start with a teeny tiny language,
• Step 2 Build a full compiler for it,
• Step 3 Add a few features,
• Go to Step 2.

(Yes, loops forever, but we will hit Ctrl-C in 10 weeks…)

Course Outline

What will we do ?

Write a compiler for NanoML -> X86

But Rome wasn’t built in a day … and neither is any serious software.

So we will write many compilers:

• Numbers and increment/decrement
• Local Variables
• Nested Binary Operations
• Booleans, Branches and Dynamic Types
• Functions
• Tuples and Structures
• Lambdas and closures
• Types and Inference
• Garbage Collection

What will you learn ?

Core principles of compiler construction

• Managing Stacks & Heap
• Type Checking
• Intermediate forms
• Optimization

Several new languages

• Haskell to write the compiler
• C to write the “run-time”
• X86 compilation target

More importantly how to write a large program

• How to use types for design
• How to add new features / refactor
• How to test & validate

What do you need to know ?

This 131 depends very heavily on CSE 130

• Familiarity with Functional Programming and Ocaml
• Datatypes (e.g. Lists, Trees, ADTs)
• Polymorphism
• Recursion
• HOFs (e.g. map, filter, fold)

Also depends on CSE 30

• Experience with some C programming
• Experience with some assembly (x86)

A few words on the medium of instruction

We will use Haskell which, for our purposes is like Ocaml but with nicer syntax.

Haskell has many advanced features beyond what we saw in 130, but we won’t be using them; in the few cases we do, I’ll explain them as we go.

Here are some links to get you started:

• Haskell for Ocaml Programmers
• Hoogle: Type-based API Search

Lets Go!