set-dispatch-macro-character

(set-dispatch-macro-character disp-char sub-char function &optional readtable)

Lite stub: accepted and ignored, returning t — user dispatch macros cannot extend the Java-side reader.

Two dispatch syntaxes that libraries define this way are built into the reader instead, so those libraries work unchanged: #N@(...) (ironclad's s-box literal, read as a vector of the given element width) and #L(...) (iterate's numbered-argument lambda: #L(list !2 !3) reads as #'(lambda (!1 !2 !3) (list !2 !3)), the arity being the highest !n the body mentions unless #nL spells it out). Any OTHER dispatch character stays unhandled, and its literals reach the ordinary reader.