code: private Environment checkDebug(Stmt.Debug stmt, Environment environment, EnclosingScope scope) {
  		// FIXME: want to refine integer type here
  		Type std_ascii = new Type.Array(Type.Int);
  		SemanticType type = checkExpression(stmt.getOperand(), environment);
  		checkIsSubtype(std_ascii, type, environment, stmt.getOperand());
  		return environment;
  	}
docs: Type check an assume statement. This requires checking that the expression
  being printed is well-formed and has string type.
  
  @param stmt
  Statement to type check
  @param environment
  Determines the type of all variables immediately going into this
  block
  @return