Allow defs to reference other defs

asm.js

@@ -560,18 +560,15 @@ class Parser {
             this.state = State.TOP;
             return;
         }
-        const value = this.integer(token);
-        if (value == null) {
-            console.error(
-                `ERROR: Unexpected token ${token}, expected value`);
-            this.def_name = undefined;
-            this.state = State.TOP;
-            return;
-        }
         const action = {
             type: Action.DEF,
-            def: { name: this.def_name, value },
+            def: { name: this.def_name },
         };
+        const value = this.integer(token);
+        if (value != null)
+            action.def.value = value;
+        else
+            action.def.symbol = token;
         this.def_name = undefined;
         this.state = State.TOP;
         return action;
@@ -742,7 +739,9 @@ export class Assembler {
     }
 
     action_def(action) {
-        this.defs[action.def.name] = action.def.value;
+        const value = action.def.value
+              ?? this.lookup_def(action.def.symbol);
+        this.defs[action.def.name] = value;
     }
 
     action_label(action) {