setLit.lean:22:19-22:21: error: overloaded, errors 
  failed to synthesize
    EmptyCollection String
  
  Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command.
  
  Fields missing: `bytes`, `isValidUtf8`
  
  Hint: Add missing fields:
     ̲b̲y̲t̲e̲s̲ ̲:̲=̲ ̲_̲
    ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲i̲s̲V̲a̲l̲i̲d̲U̲t̲f̲8̲ ̲:̲=̲ ̲_̲ ̲
setLit.lean:24:31-24:38: error: overloaded, errors 
  failed to synthesize
    Singleton Nat String
  
  Hint: Additional diagnostic information may be available using the `set_option diagnostics true` command.
  
  24:33 `val` is not a field of structure `String`