id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	difficulty
505	permit user-defined read-syntax to restart the reader	Jim Ursetto	Jim Ursetto	"Currently, user-defined read-syntax must return a value to the reader; it cannot simply discard input completely.  A proposed solution, derived from CL reader macros (see CLHS 2.2 no.4) allows a zero-value {{{(values)}}} return to reinvoke the reader in tail position, discarding any consumed input forever.

This change permits user implementation of line comments, block comments, s-expr comments, read-time feature testing, read-time evaluation, and more; all with the existing user API.

Though a zero-value return is admittedly ugly and inefficient -- one noted luminary has rightfully referred to it as a ""festering CL pustule on the buttocks of Scheme"" -- it has the advantages of being compatible with the current API and being virtually impossible to trigger accidentally.
"	enhancement	closed	minor		core libraries	4.6.x	fixed	don't fear the reader