make-dispatch-macro-character
char &optional non-terminating-p readtable => t
char--a character.
non-terminating-p--a generalized boolean. The default is false.
readtable--a readtable. The default is the current readtable.
make-dispatch-macro-character makes char be a dispatching macro character in readtable.
Initially, every character in the dispatch table associated with the char has an associated function that signals an error of type reader-error.
If non-terminating-p is true, the dispatching macro character is made a non-terminating macro character; if non-terminating-p is false, the dispatching macro character is made a terminating macro character.
(get-macro-character #\{) => NIL, false (make-dispatch-macro-character #\{) => T (not (get-macro-character #\{)) => false
The readtable is altered.