The question seems a little misleading; in some sense, all
morphosyntactic alignments are based on semantic roles. They vary in which semantic roles they bucket together.
It may help to consider that semantic roles are really infinite. We group them together under conventional terms for sake of convenience, but each term we coin actually represents an infinite spectrum of distinct semantic roles. However, if we don't have to deal with languages that distinguish those roles, we can get away with throwing them all in a box and calling it "theme."
Just don't forget that this sleight-of-hand has occurred. For example, the semantic-role frameworks I'm familiar with would consider the "patients" in your examples to be "experiencers."
In other words, be wary of thinking about any particular semantic role as a stable, objective thing
. They're actually imaginary boxes that we've drawn in particular ways for convenience, but which could easily be drawn differently.
The system you describe sounds to me most like a fluid-S morphosyntactic alignment, which could give you behavior like this bit:
In "I showed him the bird", I am again the agent, he is the patient, and the bird is the theme. In addition, this would be the same verb as to see and to look at (the first being agentless and the second having an identical agent and patient).
FWIW, my Feayran acts somewhat close to this, except that it typically treats semantic themes
as morphosyntactic patients
, and semantic experiencers
as morphosyntactic locatives.
So you get things like:Lhujukústuholukzeì.
visible-1.AGT-CAUS-bird.PAT-male.LOCI showed him the bird.
Which has the same morphosyntactic structure as:Lujukústudokkokw.
position-1.AGT-CAUS-bird.PAT-rock.LOCI put the bird on a rock.
* Fun fact: you would only say this if the bird was concealed somewhere, and then you revealed it to someone. If the bird was up in a tree somewhere and you pointed it out to someone, you would instead say:Kujukúlkushokùoqalhèe.
looking-1.AGT-CAUS-male.PAT-bird.LATI made him look towards the bird.
Now, the other person is the patient, and the bird is a lative argument.