title: Is it possible to generate new valid test cases with ANTLR4?
body: <p>For example, I had a .g4 of calculating expressions. ANTLR4 can parse any valid input of calculation expression as a parser tree. I'm considering the following scenario.</p>
  <p><em>Without any input, is it possible to generate the new valid calculation expressions based on ANTLR4? It should be a grammar-based generator.</em></p>
  <p>Does anyone have a suggestion about how to build a grammar-based generator with ANTLR4?
  Thanks in advance!</p>