When trying to port SRFI-207 to Chicken 5.2.0, I am getting many
warnings about invalid types, such as the one I quote below.

I have logged the details here:

  https://github.com/diamond-lizard/srfi-207/issues/1

The GitHub repo which contains the reference implementation port to
Chicken 5 that generated these warnings is here:

  https://github.com/diamond-lizard/srfi-207/

Here is a sample of the kind of warning I'm getting:

Warning: Invalid argument
  In file `srfi/207/parse.scm:88',
  In module `srfi-207',
  In procedure `read-textual-bytestring',
  In procedure call:

    (scheme#car 0)

  Argument #1 to procedure `car' has an invalid type:

    fixnum

  The expected type is:

    pair

  This is the expression:

    0

  Procedure `car' from module `scheme' has this type:

    ((pair 'a *) -> 'a)