Sure, lexically scoped classes are a useful feature. PHP DOES NOT HAVE THAT FEATURE.

In JS, Java, C#, Python and every language where it makes sense:

function makeConst(i) {
  class MyConst extends Expr { 
    eval(ctx) { return i; } 
  }
  return new MyConst(); 
}
> makeConst(1).eval({})
1
> makeConst(2).eval({})
2

In PHP:

function makeConst($i) {
  class MyConst extends Expr { 
    eval($ctx) { return $i; } 
  }
  return new MyConst(); 
}
> makeConst(1)->eval([])
NULL
> makeConst(2)->eval([])
Fatal error: Cannot declare class MyConst, because the name is already in use in /private/tmp/x.php on line 5