So far, we have lib/arc-read.pack and lib/parser.arc, both in anarki, as well as lib/parsecomb.arc. Not only do you have your reader, but you have a choice of them too!
arc-read seems to be designed for easy extensibility although I haven't tried it at all. (If I had looked carefully before embarking upon parser.arc, I might have saved myself a lot of trouble).
parser.arc doesn't support the full range of scheme numbers, nor does it support |foo| symbol syntax yet, apart from ||. I'm working on a new version that will hopefully be faster - welder depends on the tokeniser for syntax highlighting.
parsecomb.arc, if I understand correctly, isn't an arc parser but a library for building parsers.
In any case, having an implementation of 'read in arc makes a lot of sense, and it's in the todo at the top of arc.arc