message: Make FunctionError private
diff: @@ -43,7 +43,7 @@ use crate::{
  };
  #[derive(Debug, Clone, Error)]
  -pub(crate) enum FunctionError {
  +enum FunctionError {
  #[error("Missing parameter `{name}` for call to {function}")]
  MissingParameter { name: String, function: String },
  #[error("Found {count} extra positional parameter(s) for call to {function}")]
  