Refactor: Implement AST parser and generator

transpiler.js

@@ -1,18 +1,56 @@
+import nearley from 'nearley';
+import grammar from './grammar.js';
+
 /**
- * Transpiles a string of Hi source code into JavaScript.
+ * Generates JavaScript code from a Hi AST.
+ * @param {object} ast The Abstract Syntax Tree.
+ * @returns {string} The equivalent JavaScript code.
+ */
+function generate(ast) {
+    const generator = {
+        Program: (node) => node.body.map(generate).join('\n'),
+        Comment: (node) => node.value,
+        VariableDeclaration: (node) => `let ${node.identifier} = ${generate(node.value)};`,
+        Assignment: (node) => `${node.identifier} = ${generate(node.value)};`,
+        OutputCall: (node) => `console.log(${node.arguments.map(generate).join(', ')});`,
+        NumericLiteral: (node) => node.value,
+        StringLiteral: (node) => node.value,
+    };
+
+    if (!generator[ast.type]) {
+        throw new Error(`Unknown AST node type: ${ast.type}`);
+    }
+    return generator[ast.type](ast);
+}
+
+/**
+ * Transpiles a string of Hi source code into JavaScript using an AST.
  * @param {string} sourceCode The Hi source code.
  * @returns {string} The equivalent JavaScript code.
  */
 export function hi2js(sourceCode) {
-  // This will be replaced by a proper AST-based generator.
-  return sourceCode
-    // Comments: // ...
-    .replace(/^\s*\/\/.*/gm, (match) => match)
-    // Declaration: name: value -> let name = value;
-    .replace(/^(?!.*\/\/.*)([\w$]+)\s*:\s*(.*)/gm, 'let $1 = $2;')
-    // Assignment: name = value -> name = value;
-    .replace(/^(?!.*\/\/.*)([\w$]+)\s*=\s*([^:;].*)/gm, '$1 = $2;')
-    // Global output: _(...) -> console.log(...);
-    .replace(/^(?!.*\/\/.*)\s*_\((.*)\)/gm, 'console.log($1);');
-}
+    // 1. Create a nearley parser instance from our compiled grammar
+    const parser = new nearley.Parser(nearley.Grammar.fromCompiled(grammar));
 
+    try {
+        // 2. Feed the source code to the parser
+        parser.feed(sourceCode);
+
+        // 3. Check for ambiguity and get the AST
+        if (parser.results.length > 1) {
+            console.warn("Master, the grammar is ambiguous. Using the first parse tree.");
+        }
+        if (parser.results.length === 0) {
+            throw new Error("Unexpected end of input. The code is incomplete.");
+        }
+        const ast = parser.results[0];
+
+        // 4. Generate JavaScript from the AST
+        return generate(ast);
+
+    } catch (err) {
+        // Provide a more helpful error message
+        const message = err.message.replace(/ Instead, I found a "[^"]+" token here:/, ".");
+        throw new Error(`Parsing error: ${message}`);
+    }
+}