Senior LevelJavaScript & TypeScript
How to construct domain-specific languages (DSL) or AST parsers in JavaScript/TypeScript?
❓ Interview Prompt: Explain Lexical Analysis (tokenization), Parsing (Abstract Syntax Tree generation), and AST Evaluation.
Building a custom interpreter or domain-specific language (DSL) follows a 3-stage compiler architecture:
1. Lexer (Tokenizer):
Converts raw source code strings into a stream of structured Tokens ({ type: 'NUMBER', value: '42' }).
2. Parser:
Processes tokens and builds a hierarchical Abstract Syntax Tree (AST) representing code syntax rules.
3. Interpreter / Evaluator:
Traverses the AST nodes recursively to evaluate operations and execute instructions.
Code Implementation Example
typescript
type Token = { type: 'NUMBER' | 'PLUS'; value: string };
type ASTNode = { type: 'BinaryExpr'; left: number; right: number };
// Simple Lexer
function tokenize(code: string): Token[] {
return code.split(' ').map(str => {
if (str === '+') return { type: 'PLUS', value: '+' };
return { type: 'NUMBER', value: str };
});
}
// Simple Evaluator
function evaluate(node: ASTNode): number {
switch (node.type) {
case 'BinaryExpr': return node.left + node.right;
}
}💡Basic Lexer tokenization and AST node evaluation architecture.
🎯 Interview Key Takeaway
Custom DSL engines use a Lexer to produce tokens, a Parser to construct an AST, and an Evaluator to execute logic.
#AST#Parsing#Compilers#DSL#Senior
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