diff --git a/src/engine/parser.ts b/src/engine/parser.ts
index ace0915..a8b2d06 100644
--- a/src/engine/parser.ts
+++ b/src/engine/parser.ts
@@ -217,136 +217,129 @@ class Parser {
 
     if (!lhs) return null;
 
-    loop: for (;;) {
+    for (;;) {
       tk = this.peek();
       if (!tk) break;
 
-      switch (tk.t) {
-        case "percent": {
-          if (PREC.POSTFIX < minPrec) break loop;
-          this.i++;
-          lhs = { k: "pct", x: lhs };
-          continue loop;
-        }
-        case "bang": {
-          if (PREC.POSTFIX < minPrec) break loop;
-          this.i++;
-          lhs = { k: "fact", x: lhs };
-          continue loop;
-        }
-        case "unit": {
-          if (PREC.POSTFIX < minPrec) break loop;
-          this.i++;
-          lhs = { k: "unit", x: lhs, unit: tk.unit };
-          continue loop;
-        }
-        case "currency": {
-          if (PREC.POSTFIX < minPrec) break loop;
-          this.i++;
-          lhs = { k: "curr", x: lhs, code: tk.code };
-          continue loop;
-        }
-        case "scale": {
-          if (PREC.POSTFIX < minPrec) break loop;
-          this.i++;
-          lhs = { k: "scale", x: lhs, mult: tk.mult, label: "" };
-          continue loop;
-        }
-        case "op": {
-          switch (tk.op) {
-            case "pow": {
-              if (PREC.POW < minPrec) break loop;
-              const save = this.i;
-              this.i++;
-              const r = this.parseExpr(PREC.POW);
-              if (!r) { this.i = save; break loop; }
-              lhs = { k: "bin", op: "pow", l: lhs, r };
-              continue loop;
-            }
-            case "mul":
-            case "div":
-            case "mod": {
-              if (PREC.MUL < minPrec) break loop;
-              const save = this.i;
-              this.i++;
-              const r = this.parseExpr(PREC.MUL + 1);
-              if (!r) { this.i = save; break loop; }
-              lhs = { k: "bin", op: tk.op, l: lhs, r };
-              continue loop;
-            }
-            case "plus":
-            case "minus": {
-              if (PREC.ADD < minPrec) break loop;
-              const save = this.i;
-              this.i++;
-              const r = this.parseExpr(PREC.ADD + 1);
-              if (!r) { this.i = save; break loop; }
-              lhs = { k: "bin", op: tk.op, l: lhs, r };
-              continue loop;
-            }
+      const nextLhs = this.parseExprStep(tk, lhs, minPrec);
+      if (nextLhs === undefined) break;
+      lhs = nextLhs;
+    }
+    return lhs;
+  }
+
+  private parseExprStep(tk: Token, lhs: Node, minPrec: number): Node | undefined {
+    switch (tk.t) {
+      case "percent": {
+        if (PREC.POSTFIX < minPrec) return undefined;
+        this.i++;
+        return { k: "pct", x: lhs };
+      }
+      case "bang": {
+        if (PREC.POSTFIX < minPrec) return undefined;
+        this.i++;
+        return { k: "fact", x: lhs };
+      }
+      case "unit": {
+        if (PREC.POSTFIX < minPrec) return undefined;
+        this.i++;
+        return { k: "unit", x: lhs, unit: tk.unit };
+      }
+      case "currency": {
+        if (PREC.POSTFIX < minPrec) return undefined;
+        this.i++;
+        return { k: "curr", x: lhs, code: tk.code };
+      }
+      case "scale": {
+        if (PREC.POSTFIX < minPrec) return undefined;
+        this.i++;
+        return { k: "scale", x: lhs, mult: tk.mult, label: "" };
+      }
+      case "op": {
+        switch (tk.op) {
+          case "pow": {
+            if (PREC.POW < minPrec) return undefined;
+            const save = this.i;
+            this.i++;
+            const r = this.parseExpr(PREC.POW);
+            if (!r) { this.i = save; return undefined; }
+            return { k: "bin", op: "pow", l: lhs, r };
           }
-          break loop;
-        }
-        case "pctop": {
-          if (tk.op === "of" || tk.op === "off" || tk.op === "on") {
-            if (!(lhs.k === "pct" || lhs.k === "var" || lhs.k === "pctop")) {
-              this.i++;
-              continue loop;
-            }
-            if (PREC.MUL < minPrec) break loop;
+          case "mul":
+          case "div":
+          case "mod": {
+            if (PREC.MUL < minPrec) return undefined;
             const save = this.i;
             this.i++;
             const r = this.parseExpr(PREC.MUL + 1);
-            if (!r) { this.i = save; break loop; }
-            lhs = { k: "pctop", op: tk.op, l: lhs, r };
-            continue loop;
+            if (!r) { this.i = save; return undefined; }
+            return { k: "bin", op: tk.op, l: lhs, r };
           }
-          if (tk.op.startsWith("as_pct") || tk.op.endsWith("what_is")) {
-            if (PREC.CONV < minPrec) break loop;
+          case "plus":
+          case "minus": {
+            if (PREC.ADD < minPrec) return undefined;
             const save = this.i;
             this.i++;
-            const r = this.parseExpr(PREC.ADD);
-            if (!r) { this.i = save; break loop; }
-            lhs = { k: "pctop", op: tk.op, l: lhs, r };
-            continue loop;
+            const r = this.parseExpr(PREC.ADD + 1);
+            if (!r) { this.i = save; return undefined; }
+            return { k: "bin", op: tk.op, l: lhs, r };
           }
-          break loop;
-        }
-        case "lparen":
-        case "const":
-        case "func":
-        case "word": {
-          if (tk.t === "word" && !this.vars.has(tk.raw)) break loop;
-          if (PREC.MUL < minPrec) break loop;
-          const save = this.i;
-          const r = this.parseExpr(PREC.MUL + 1);
-          if (!r) { this.i = save; break loop; }
-          lhs = { k: "bin", op: "mul", l: lhs, r };
-          continue loop;
-        }
-        case "bitop": {
-          if (PREC.BIT < minPrec) break loop;
-          const save = this.i;
-          this.i++;
-          const r = this.parseExpr(PREC.BIT + 1);
-          if (!r) { this.i = save; break loop; }
-          lhs = { k: "bit", op: tk.op, l: lhs, r };
-          continue loop;
-        }
-        case "conv": {
-          if (PREC.CONV < minPrec) break loop;
-          const save = this.i;
-          this.i++;
-          const target = this.parseTarget();
-          if (!target) { this.i = save; break loop; }
-          lhs = { k: "conv", x: lhs, target: this.tryHistoricalDate(target) };
-          continue loop;
         }
+        return undefined;
       }
-
-      break;
+      case "pctop": {
+        if (tk.op === "of" || tk.op === "off" || tk.op === "on") {
+          if (!(lhs.k === "pct" || lhs.k === "var" || lhs.k === "pctop")) {
+            this.i++;
+            return lhs;
+          }
+          if (PREC.MUL < minPrec) return undefined;
+          const save = this.i;
+          this.i++;
+          const r = this.parseExpr(PREC.MUL + 1);
+          if (!r) { this.i = save; return undefined; }
+          return { k: "pctop", op: tk.op, l: lhs, r };
+        }
+        if (tk.op.startsWith("as_pct") || tk.op.endsWith("what_is")) {
+          if (PREC.CONV < minPrec) return undefined;
+          const save = this.i;
+          this.i++;
+          const r = this.parseExpr(PREC.ADD);
+          if (!r) { this.i = save; return undefined; }
+          return { k: "pctop", op: tk.op, l: lhs, r };
+        }
+        return undefined;
+      }
+      case "lparen":
+      case "const":
+      case "func":
+      case "word": {
+        if (tk.t === "word" && !this.vars.has(tk.raw)) return undefined;
+        if (PREC.MUL < minPrec) return undefined;
+        const save = this.i;
+        const r = this.parseExpr(PREC.MUL + 1);
+        if (!r) { this.i = save; return undefined; }
+        return { k: "bin", op: "mul", l: lhs, r };
+      }
+      case "bitop": {
+        if (PREC.BIT < minPrec) return undefined;
+        const save = this.i;
+        this.i++;
+        const r = this.parseExpr(PREC.BIT + 1);
+        if (!r) { this.i = save; return undefined; }
+        return { k: "bit", op: tk.op, l: lhs, r };
+      }
+      case "conv": {
+        if (PREC.CONV < minPrec) return undefined;
+        const save = this.i;
+        this.i++;
+        const target = this.parseTarget();
+        if (!target) { this.i = save; return undefined; }
+        return { k: "conv", x: lhs, target: this.tryHistoricalDate(target) };
+      }
+      default:
+        return undefined;
     }
-    return lhs;
   }
   /** If the current token is `pctop(on)` + `datelit`, consume them and attach `onDate`. */
   private tryHistoricalDate(target: ConvTarget): ConvTarget {