Mini Compiler — Stanley Wang

about

The compiler was built for COMP 520, taught in Winter 2026 by Professor Christophe Dubach.

Any code you write is live-compiled directly in your browser, made possible by TeaVM, which transpiles my compiler's Java source code into minified JavaScript.

main.c

void main() {
  print_s((char*)"Hello, world!\n");
}

hello.txt

This is an interactive demonstration of a C compiler I created as part of McGill's Compiler Design course. By live-compiling code in your browser and stepping through each stage of compilation in an intuitive and educational way, I hope to show how source code is actually translated into assembly, and the often beautiful, often monstrous journey that it is. Please enjoy! Stanley

mini-c.txt

Declarations

void main() {
  int x;
  int y;
  // rest of function
  x = 4;
  ...
}

int x = 4;

Loops

There is no for, do or switch.

i = 0;
while (i < 10) {
  i = i + 1;
}

Operators

// arithmetic
x = a + b - c * d / e % f;
x = -a;
// comparison and logic
y = a < b || a <= b || a > b;
y = a >= b && a == b && a != b;
// address and dereference
p = &x;
x = *p;
// fields and indexing
x = s.f + arr[0];
// sizeof and casts
x = sizeof(int) + (int)'c';

Field access

// s is a struct
s.field = 1;
// p points to a struct
(*p).field = 1;

p->field = 1;

Types

int, char and void, structs, pointers and arrays.

struct node {
  int value;
  struct node* next;
};
char name[8];

Built-ins

In place of the standard library:

// prints a string: (char*)"hi"
void print_s(char* s);
// prints an int
void print_i(int i);
// prints a char
void print_c(char c);
// reads a char from input
char read_c();
// reads an int from input
int read_i();
// allocates memory; cast it
void* mcmalloc(int size);

malloc(size);
printf(format, ...);

ast.txt

declarations

Introduce a name: a variable, a struct's field, a function, or a struct or class type.

variable
field
function
prototype
struct
class

statements

The steps a function takes. Each starts with a keyword, is a block in braces, or is an expression ended by ;.

block
while
if
return
continue
break
expression

expressions

Anything that works out to a value: a number, a name, a call, or operators on other expressions.

number
character
string
name
call
operator
assignment
index
field
value at
address of
sizeof
cast
new
method call