This content originally appeared on DEV Community and was authored by Sh Raj
Creating a C compiler in JavaScript is a complex and ambitious project that involves several components, including lexical analysis, parsing, semantic analysis, and code generation. Below is a simplified and high-level example of how you might start building such a compiler. This example will focus on the lexical analysis (tokenization) and parsing stages, which are the first steps in compiling C code.
Step 1: Lexical Analysis (Tokenization)
The lexical analyzer (lexer) converts the input C code into a stream of tokens.
class Lexer {
constructor(input) {
this.input = input;
this.tokens = [];
this.current = 0;
}
tokenize() {
while (this.current < this.input.length) {
let char = this.input[this.current];
if (/\s/.test(char)) {
this.current++;
continue;
}
if (/[a-zA-Z_]/.test(char)) {
let start = this.current;
while (/[a-zA-Z0-9_]/.test(this.input[this.current])) {
this.current++;
}
this.tokens.push({ type: 'IDENTIFIER', value: this.input.slice(start, this.current) });
continue;
}
if (/[0-9]/.test(char)) {
let start = this.current;
while (/[0-9]/.test(this.input[this.current])) {
this.current++;
}
this.tokens.push({ type: 'NUMBER', value: this.input.slice(start, this.current) });
continue;
}
switch (char) {
case '+':
this.tokens.push({ type: 'PLUS', value: '+' });
this.current++;
break;
case '-':
this.tokens.push({ type: 'MINUS', value: '-' });
this.current++;
break;
case '*':
this.tokens.push({ type: 'STAR', value: '*' });
this.current++;
break;
case '/':
this.tokens.push({ type: 'SLASH', value: '/' });
this.current++;
break;
case '=':
this.tokens.push({ type: 'EQUAL', value: '=' });
this.current++;
break;
case ';':
this.tokens.push({ type: 'SEMICOLON', value: ';' });
this.current++;
break;
case '(':
this.tokens.push({ type: 'LPAREN', value: '(' });
this.current++;
break;
case ')':
this.tokens.push({ type: 'RPAREN', value: ')' });
this.current++;
break;
default:
throw new TypeError('Unexpected character: ' + char);
}
}
return this.tokens;
}
}
Step 2: Parsing
The parser converts the stream of tokens into an abstract syntax tree (AST).
class Parser {
constructor(tokens) {
this.tokens = tokens;
this.current = 0;
}
parse() {
let ast = {
type: 'Program',
body: []
};
while (this.current < this.tokens.length) {
ast.body.push(this.parseStatement());
}
return ast;
}
parseStatement() {
let token = this.tokens[this.current];
if (token.type === 'IDENTIFIER' && this.tokens[this.current + 1].type === 'EQUAL') {
return this.parseAssignment();
}
throw new TypeError('Unknown statement: ' + token.type);
}
parseAssignment() {
let identifier = this.tokens[this.current];
this.current++; // skip identifier
this.current++; // skip equal sign
let value = this.parseExpression();
this.expect('SEMICOLON');
return {
type: 'Assignment',
identifier: identifier.value,
value: value
};
}
parseExpression() {
let token = this.tokens[this.current];
if (token.type === 'NUMBER') {
this.current++;
return {
type: 'Literal',
value: Number(token.value)
};
}
throw new TypeError('Unknown expression: ' + token.type);
}
expect(type) {
let token = this.tokens[this.current];
if (token.type !== type) {
throw new TypeError('Expected ' + type + ' but found ' + token.type);
}
this.current++;
}
}
Step 3: Code Generation
Finally, the code generator converts the AST into the target language, which could be JavaScript or any other language.
class CodeGenerator {
generate(node) {
switch (node.type) {
case 'Program':
return node.body.map(statement => this.generate(statement)).join('\n');
case 'Assignment':
return `let ${node.identifier} = ${this.generate(node.value)};`;
case 'Literal':
return node.value;
default:
throw new TypeError('Unknown node type: ' + node.type);
}
}
}
Putting It All Together
Here is how you might use the lexer, parser, and code generator:
const input = `x = 42;`;
const lexer = new Lexer(input);
const tokens = lexer.tokenize();
console.log('Tokens:', tokens);
const parser = new Parser(tokens);
const ast = parser.parse();
console.log('AST:', JSON.stringify(ast, null, 2));
const generator = new CodeGenerator();
const output = generator.generate(ast);
console.log('Output:', output);
This will tokenize the input, parse it into an AST, and generate JavaScript code from the AST.
Note
This example is highly simplified and only handles a tiny subset of the C language. A full-fledged C compiler would require handling a much larger set of tokens, parsing complex expressions, statements, declarations, types, and generating more sophisticated code.
This content originally appeared on DEV Community and was authored by Sh Raj
Sh Raj | Sciencx (2024-06-30T03:57:33+00:00) Creating a C compiler in JavaScript. Retrieved from https://www.scien.cx/2024/06/30/creating-a-c-compiler-in-javascript/
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