wasmc

A toy compiler for a subset of C to WebAssembly

Quick Example

/* main.wasmc */
int main() {
    log("Hello world from WebAssembly!\n");
}

# command line
$ ts-node src/compile.ts main.wasmc -o main.wasm
$ ts-node src/run.ts main.wasm
> Hello world from WebAssembly!

Overview

wasmc supports most basic features of C, although a few are still being added:

Function Definition

/* <type> <identifier> (<param>, ...) { <statement>* } */

char* fn_name (char* ptr, int sz) { ... }

Variables

/* Declaration
 * <type> <identifier> <array-expression>? ;
 * <type> <identifier> = <expr> ;
 */

int x;
int arr[25];
int y = 5;

/* Set value of a variable
 * <identifier> <array-expression>? = <expr> */
x = 25;
y = (9 * 46);
arr[2] = (99 + 4);

If/Else

/* 
 * if (<expr>) { <statement>* }
 * if (<expr>) { <statement>* } else { <statement>* }
 * if (<expr>) { <statement>* } else <if-statement>+
 */

if (x > 0) {
    x = x + 1;
} else {
    return;
}

Loops

/* while (<expr>) { <statement>* } */

int x = 10;
while (x > 0) {
    if (x == 5) {
        // Don't print 5
        x--;
        continue;
    }
    logInt(x);
    x--;

    if (x < 2) {
        // Exit loop early
        break;
    }
}

/* do-while { <statement>* } (<expr>); */

int x = 10;
do {
  logInt(x);
  x--;
} while (x > 0);

/* for (<variable-dec>?; <expr>?; <statement>?) { <statement>* } */

for (int x = 10; x > 0; x--) {
  logInt(x);
}

Operators

Supported binary operators: +, -, *, /, >, <, >=, <=, ==, !=, &&, &, ||, |, ^

Assignment operators: +=, -=, *=, /=, &=, |=, ^=

Unary operators: ++, --, !, *, &; todo: ~, type casts, sizeof

Provided Functions

Currently only: void log(char*) for strings and void logInt(int) for integers.

Setup

Install https://github.com/WebAssembly/wabt. I know this is clunky, I will find a way to streamline this eventually. The compiler depends on wast2wasm being in your $PATH.

# ts-node is the easiest way, but you can also use tsc to compile, then run js from dist/ folder
npm i -g typescript ts-node  # Or install these locall only, if you want
npm i

Compiler

ts-node src/compile.ts [filename] <opts>

Opts:

• -o output filename, defaults to a.out.wasm
• -S generate wast only (default filename a.out.wast)
• -i keep intermediate wast
• -r immediately run generated wasm
• -d debug

WASM Runner

ts-node src/run.ts [filename]

Roadmap

• Proper array sizes (they're all 8-bit currently)
• Properly implement operator precedence
  • Currently it's just in the order given, but parens are supported
  • Because of this be really careful with conditional expressions, && is currently equivalent to & and could cause confusion
• Preprocessor/multiple file support
• Support for structs
• Flesh out a std library with printf, etc
• Use a stack for local arrays; currently all arrays are stored in global memory and never freed.
• malloc/free support
• Web demo (need to figure out how to get wat2wasm running in the browser)