In Chicken 5, read/write invariance of symbols beginning with #! is violated.
> (with-input-from-string
(with-output-to-string (lambda () (write (string->symbol "#!abc")))) read)
Error: invalid `#!' token: “abc"
> (with-input-from-string
(with-output-to-string (lambda () (write (string->symbol "#!")))) read)
Error: invalid `#!' token: “"
This causes a problem with chicken-doc, as there is a syntax entry called “#!”
which is written out but cannot be read back in. In Chicken 4, this symbol is
escaped when written out and reads back in fine.
This occurs because in Chicken 5, sym-is-readable? was changed:
commit 05f341e07a179ea95d891e5c55b2fe3d0dbe1ffe
Author: Evan Hanson <ev...@foldling.org>
Date: Wed Mar 14 17:53:00 2018 +1300
Print #!-style symbols verbatim, without pipes
These symbols are readable, so should be printed as-is by `##sys#print'
just like #:keywords or the #!eof token.
- ((and (eq? c #\#)
- (not (eq? #\% (##core#inline "C_subchar"
str 1))))
- #f)
+ ((eq? c #\#) ;; #!rest, #!key etc
+ (eq? (##core#inline "C_subchar" str 1) #\!))
Unfortunately this assertion is incorrect: not all #! style symbols are
readable, only valid #! style symbols such as #!rest. Other symbols are
rejected by the reader. Furthermore, certain strange combinations, such as “(#!
(foo bar))” result in an unterminated list, no matter how many close parens are
added. The latter is the issue I am hitting.
The fix is probably to explicitly test for valid tokens, which appear to be
only: “optional”, “rest” and “key”. Probably “eof” is ok as well—not 100% sure.
The reader, of course, already tests for these exact tokens, so the writer
should too.
Alas, chicken-doc won’t work with Chicken 5 until this is fixed — I worked
around the file locking bug in 5.0.0, but the writer bug is fatal.
Jim_______________________________________________
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