Possibly missing reader macros

[phoe]

persistent-vector/persistent-vector.lisp

Lines 499 to 518 in 29974e8

	(defmethod print-object ((vec vector-trie) stream)
	(declare (type stream stream))
	(when (transient-vector-p vec)
	(write-char #\#)
	(write-char #\T))
	(let ((len (vec-count vec)))
	(declare (type fixnum len))
	(if (> len *max-print-vec-length*)
	(progn
	(format stream "#S(~A|length:~a)" (type-of vec) len))
	(progn (write-char #\[ stream)
	(loop with itr = (vec-make-iterator vec)
	for (remaining val) = (multiple-value-list (funcall itr))
	then (list next-remaining next-val)
	while remaining
	for (next-remaining next-val) = (multiple-value-list (funcall itr))
	do (prin1 val stream)
	(when next-remaining (write-char #\ stream)))
	(write-char #\] stream)))))

Where are the reader macros for #T and [ defined, in order to read these objects back into Lisp? I cannot see them anywhere. It would be good to depend on named-readtables and define a custom readtable including these macro characters for easy readtable composition, too.

[DanielKeogh]

I like reader macro's, but I'm not planning on adding them to this library yet. Maybe later.

[phoe]

In that case, printing via #T and [ should be deferred until then - otherwise, print-read consistency is violated, and e.g. an empty set [] is going to be read as a symbol with name [].

[DanielKeogh]

Huh. I never heard of print-read consistency before this. I can go down that path, although I'm really keen to avoid any external dependencies.

make-hash-table breaks print-read consistency, but I guess printing "#<" at the start of your print-object is a valid work around for this?

[phoe]

Print-read consistency means that printing an object readably and then reading back the representation gives you an object equivalent to the original one.

Wrt hash tables, if you set *print-readably* to true, then you can print hash tables readably and then read them back. The way to do so is implementation-dependent, but it works.

Using #< at the beginning of a printed representation means that an object is printed in an unreadable form; if *print-readably* is set to true, then this instead signals an error at printing time.

[DanielKeogh]

Ok. I'll get on this then. Thanks.

[DanielKeogh]

I added some reader macros, and changed print so that it prints persistent-vector only, because nobody should be printing transient vectors anyway.
Also made *print-readably* clobber *print-length* because that seems to be the default behaviour of other print-object implementations.

I'm so-so about making print-object signal an error if someone hasn't turned on the associated reader macro.

I'm not going to use named-readtables here, because I want to have zero external dependencies for this library. The ultimate goal is to have a bunch of libs like this in a suite with a pile of utilities, and I expect I will use named-readtables in that case.