Tabloid Feature: Add parent scope variable reassignment!

README.md

@@ -34,6 +34,13 @@ Tabloid supports binary infix operators for arithmetic and logic.
 
 `IS ACTUALLY` is a way to test equality, like `==` in most other languages. We can also make comparisons with `X BEATS Y` (`x > y`) and `X SMALLER THAN Y` (`x < y`).
 
+We can initialize and assign variables in the current scope with `EXPERTS CLAIM...TO BE`, and reassign variables using `EVIDENCE SHOWS...TO BE`.
+
+```
+EXPERTS CLAIM your_mom TO BE 'big'
+EVIDENCE SHOWS your_mom TO BE 'massive'
+```
+
 We can print the result of any expression with `YOU WON'T WANT TO MISS`. You won't want to miss what you're printing, and now you never will!
 
 ```

static/js/lang.js

@@ -110,6 +110,7 @@ const T = {
     LiesBang: Symbol('LiesBang'),
     EndOfStory: Symbol('EndOfStory'),
     ExpertsClaim: Symbol('ExpertsClaim'),
+    EvidenceShows: Symbol('EvidenceShows'),
     ToBe: Symbol('ToBe'),
     YouWontWantToMiss: Symbol('YouWontWantToMiss'),
     LatestNewsOn: Symbol('LatestNewsOn'),
@@ -189,6 +190,11 @@ function tokenize(prog) {
                 tokens.push(T.ExpertsClaim);
                 break;
             }
+            case 'EVIDENCE': {
+                reader.expect('SHOWS');
+                tokens.push(T.EvidenceShows);
+                break;
+            }
             case 'TO': {
                 reader.expect('BE');
                 tokens.push(T.ToBe);
@@ -477,6 +483,17 @@ class Parser {
                 name,
                 val,
             }
+        } else if (next === T.EvidenceShows) {
+            // assignment
+            const name = this.expectIdentString();
+            this.tokens.expect(T.ToBe);
+            const val = this.expr();
+            return {
+                type: N.Assignment,
+                name,
+                val,
+                lookup: true,
+            }
         } else if (next === T.ShockingDevelopment) {
             // return
             return {
@@ -613,7 +630,16 @@ class Environment {
                 throw new Error(`Runtime error: Undefined variable "${node.val}"`);
             }
             case N.Assignment: {
-                scope[node.name] = this.eval(node.val);
+                if (node.lookup) {
+                    let i = this.scopes.length - 1;
+                    while (i >= 0) {
+                        if (node.name in this.scopes[i]) {
+                            return this.scopes[i][node.name] = this.eval(node.val);
+                        }
+                        i --;
+                    }
+                    throw new Error(`Runtime error: Variable "${node.name}" does not exist`);
+                } else scope[node.name] = this.eval(node.val);
                 return scope[node.name];
             }
             case N.BinaryOp: {

static/js/main.js

@@ -271,7 +271,11 @@ class App extends Component {
                 </li>
                 <li>
                     <code class="inline fixed block">EXPERTS CLAIM...TO BE</code>
-                    declare or assign to a variable
+                    declare or assign to a variable (in the current scope)
+                </li>
+                <li>
+                    <code class="inline fixed block">EVIDENCE SHOWS...TO BE</code>
+                    reassign a variable
                 </li>
                 <li>
                     <code class="inline fixed block">YOU WON'T WANT TO MISS</code>