Many practical applications of eval() boil down to accessing (and perhaps manipulating) scopes in a manner which the host language does not normally allow. Likewise, many potential dangers or pitfalls of eval() relate to how it allows (or does not allow) dynamically-assembled code to inherit access to some spatial or temporal scope of variables, definitions, "unsafe" libraries, and so forth. The interaction of eval() with scope is much a much more interesting design question than whether it accepts an AST, a string, or something in-between, except to the extent that non-stringy "programs" represent some form of reified closure.