sexpr: the reduce code in eval should not modify the value of a struct val
sexpr: the reduce code in eval should not modify the value of a struct val

Values are immutable.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc