diff --git a/src/execute/lex-pipe.ts b/src/execute/lex-pipe.ts
index 897a0b6d..cdb8f71d 100644
--- a/src/execute/lex-pipe.ts
+++ b/src/execute/lex-pipe.ts
@@ -52,6 +52,13 @@ export class LexPipe extends Frame implements IFinish, IPerformer {
           break
         }
         case 'pop': {
+          if (this.level === 0) {
+            console.error('LexPipe.perform.pop.failed: already at top level')
+            break
+          }
+          if (!parser.canPop(value)) {
+            break
+          }
           const next_parser = parser.pop(value)
           this.set(Frame.kOUT, next_parser)
           this.level -= 1
diff --git a/src/execute/parse-pipe.ts b/src/execute/parse-pipe.ts
index 825df53d..efe9f76b 100644
--- a/src/execute/parse-pipe.ts
+++ b/src/execute/parse-pipe.ts
@@ -35,14 +35,18 @@ export class ParsePipe extends FrameArray implements IFinish {
 
   public pop (Factory: any): Frame {
     const parent = this.get(ParsePipe.kOUT) as ParsePipe
-    if (parent.Factory !== Factory) {
-      const msg = [' open:', parent.Factory, ' close:', Factory]
-      console.error('pop.mismatched-brackets' + msg.join(''))
-    }
     this.finish(Frame.nil)
     return parent
   }
 
+  public canPop (Factory: any): boolean {
+    const match = (this.Factory.name === Factory.name)
+    if (!match) {
+      console.error(`ParsePipe.canPop.failed: ${Factory.name} cannot pop ${this.Factory.name}`)
+    }
+    return match
+  }
+
   public finish (terminal: any): Frame {
     this.next()
     const out = this.get(Frame.kOUT)
diff --git a/test/execute/evaluate-spec.ts b/test/execute/evaluate-spec.ts
index a78fb992..139d264b 100644
--- a/test/execute/evaluate-spec.ts
+++ b/test/execute/evaluate-spec.ts
@@ -85,5 +85,35 @@ describe('evaluate', () => {
       const output = result.at(0)
       expect(output).to.be.instanceof(frame.FrameLazy)
     })
+
+    it('returns FrameNote for empty ()', () => {
+      const result = evaluate('()')
+      const output = result.at(0)
+      expect(output).to.be.instanceof(frame.FrameNote)
+    })
+
+    it('returns FrameArray for empty [] with spaces', () => {
+      const result = evaluate('  [  ]  ')
+      const output = result.at(0)
+      expect(output).to.be.instanceof(frame.FrameArray)
+    })
+
+    it('returns FrameArray for empty [] with comments', () => {
+      const result = evaluate('[#comment#]')
+      const output = result.at(0)
+      expect(output).to.be.instanceof(frame.FrameArray)
+    })
+
+    it('returns FrameNote for mis-matched brackets', () => {
+      const result = evaluate('[}')
+      const output = result.at(0)
+      expect(output).to.be.instanceof(frame.FrameNote)
+    })
+
+    it('returns FrameNote for un-opened close bracket', () => {
+      const result = evaluate('}')
+      const output = result.at(0)
+      expect(output).to.be.instanceof(frame.FrameNote)
+    })
   })
 })