This project is an implementation of a PL/0 compiler written in Common Lisp. The goal is to study compiler construction by following Wirth’s classic PL/0 language, while exploring modern backends such as WebAssembly (WASM).

PL/0 is a small teaching language introduced by Niklaus Wirth in Algorithms + Data Structures = Programs (1976).

It has:

• Constants, variables, and procedures
• Arithmetic expressions and conditions
• Control flow with if and while
• Structured blocks using begin ... end

It is deliberately minimal, making it ideal for educational compiler projects.

• The language has been updated with comments (//) and types.
• The language supports explicit 32-bit integer delcarations.

// Example pl0 program
const int max = 10;

int x, y, sum;

// Procedure 'add' adds 2 integers
procedure add;
begin
   sum := x + y;
end;

// Main program block
begin
  x := 3;
  y := 5;
  call add;
end.

src/
  lexer.lisp     ; Tokenizer for PL/0 source code
  ast.lisp       ; Abstract syntax tree (AST) definitions
  parser.lisp    ; Recursive-descent parser for PL/0 grammar
  analyzer.lisp  : Symbol table generator and symantic checking
  emitter.lisp   ; Code generator for IR / WASM
  main.lisp      ; Main program driver

tests/
  *.pl0          ; Example PL/0 programs for testing

• Common Lisp implementation (tested with SBCL and CCL)
• Quicklisp package manager
• SLIME for Emacs integration (recommended)

Clone the repository:

git clone https://github.com/asuttles/andy.git
cd andy

(ql:quickload :andy)
(andy.main:compile-source "tests/test1.pl0")

Niklaus Wirth, Algorithms + Data Structures = Programs, 1976

The PL/0 Grammar

For more information about the project, see Project Notes.

MIT License. See LICENSE for details.