Scheme Request for Implementation 175,
"ASCII character library,"
by Lassi Kortela,
has gone into "final" status.
The document and an archive of the discussion are available at https://srfi.schemers.org/srfi-175/.
Here's the abstract:
This SRFI defines ASCII-only equivalents to many of the character procedures in standard Scheme plus a few extra ones. Recent Scheme standards are based around Unicode but the significant syntactic elements in many file formats and network protocols are all ASCII. Such low-level code can run faster and its behavior can be easier to understand when it uses ASCII primitives.
Here are the diffs since the most recent draft:
Many thanks to Lassi and to everyone who contributed to the discussion of this SRFI.