code: private Environment checkAssert(Stmt.Assert stmt, Environment environment, EnclosingScope scope) {
  		return checkCondition(stmt.getCondition(), true, environment);
  	}
docs: Type check an assertion statement. This requires checking that the expression
  being asserted is well-formed and has boolean type. An assert statement can
  affect the resulting environment in certain cases, such as when a type test
  is assert. For example, after <code>assert x is int</code> the environment
  will regard <code>x</code> as having type <code>int</code>.
  
  @param stmt
  Statement to type check
  @param environment
  Determines the type of all variables immediately going into this
  block
  @return