A literal is implicitly a symbolic address and a constant-generation request; nesting those functions in other expressions was considered a bit too much extra work for ASMH, from which HLASM was derived. And there were no strong requests for forms such as A(=X'zzz') during the first six HLASM releases.
As I remember, the problem with adcons containing literals is that they can lead to recursions such as A(=A(...)) and the like. John Ehrman
