>>> I think the name "ascii-horizontal-whitespace?" is far too long
>>
>> if it troubles you, you could drop "whitespace" from the name

To me, `ascii-horizontal?` says "any character that is not a newline",
i.e. including letters and numbers and stuff. I've actually had such an
`ascii-horizontal?` function in several parsers I've written, and it has
been useful. Perhaps it should be in this SRFI as well. The only trouble
is what to do about control characters (the ones that have nothing to do
with newlines or whitespace).