Disable function expressions (#96)

* Add failing test for disallowed function expression

* Disallow using old-school function definitions and named function declarations as expressions

package.json

@@ -1,6 +1,6 @@
 {
   "name": "js-slang",
-  "version": "0.1.9",
+  "version": "0.1.10",
   "description": "Javascript-based interpreter for slang, written in Typescript",
   "author": {
     "name": "Source Academy",

src/__tests__/__snapshots__/disallowed_syntax.ts.snap

@@ -8,4 +8,8 @@ exports[`Cannot leave blank expressions in for loops 3`] = `"Line 2: For stateme
 
 exports[`Cannot leave blank expressions in for loops 4`] = `"Line 2: For statement cannot have empty init,test,update expressions."`;
 
+exports[`Cannot use js function expressions 1`] = `"Line 2: Function expressions are not allowed"`;
+
 exports[`Cannot use update expressions 1`] = `"Line 3: Update expressions are not allowed"`;
+
+exports[`DEFINITELY CANNOT use named function declarations as expressions 1`] = `"Line 2: Function expressions are not allowed"`;

src/__tests__/disallowed_syntax.ts

@@ -57,3 +57,32 @@ test("Cannot use update expressions", () => {
   });
 });
 
+test("Cannot use js function expressions", () => {
+  const code = `
+  map(function(x) {
+    return x + 1;
+  }, list(1));
+  `;
+  const context = mockContext(3);
+  const promise = runInContext(code, context, { scheduler: "preemptive" });
+  return promise.then(obj => {
+    expect(obj.status).toBe("error");
+    const errors = parseError(context.errors);
+    expect(errors).toMatchSnapshot();
+  });
+});
+
+test("DEFINITELY CANNOT use named function declarations as expressions", () => {
+  const code = `
+  map(function a(x) {
+    return x + 1;
+  }, list(1));
+  `;
+  const context = mockContext(3);
+  const promise = runInContext(code, context, { scheduler: "preemptive" });
+  return promise.then(obj => {
+    expect(obj.status).toBe("error");
+    const errors = parseError(context.errors);
+    expect(errors).toMatchSnapshot();
+  });
+});

src/interpreter.ts

@@ -175,9 +175,6 @@ export const evaluators: { [nodeType: string]: Evaluator<es.Node> } = {
     }
     return res
   },
-  FunctionExpression: function*(node: es.FunctionExpression, context: Context) {
-    return new Closure(node, currentFrame(context), context)
-  },
   ArrowFunctionExpression: function*(node: es.Function, context: Context) {
     return new ArrowClosure(node, currentFrame(context), context)
   },

src/syntaxTypes.ts

@@ -11,7 +11,6 @@ const syntaxTypes: { [nodeName: string]: number } = {
   BinaryExpression: 1,
   LogicalExpression: 1,
   ConditionalExpression: 1,
-  FunctionExpression: 1,
   ArrowFunctionExpression: 1,
   Identifier: 1,
   Literal: 1,
@@ -45,7 +44,9 @@ const syntaxTypes: { [nodeName: string]: number } = {
   CatchClause: Infinity,
   DoWhileStatement: Infinity,
   ForInStatement: Infinity,
-  SequenceExpression: Infinity
+  SequenceExpression: Infinity,
+  FunctionExpression: Infinity,
+
 }
 
 export default syntaxTypes