No more Refs, no more store, every top level def goes in the store, to update store values use :=

src/parser.ts

@@ -152,6 +152,14 @@ export class Parser {
 
         let expr = this.parseInfix();
 
+        // Rebind
+        if (this.current().kind == 'colon-equals') {
+            const token = this.current();
+            this.advance();
+            const value = this.parseExpression();
+            return { kind: 'rebind', target: expr, value, ...this.getPos(token) };
+        }
+
         // Match
         if (this.current().kind === 'pipe') {
             return this.parseMatch(expr);