Viterbi algorithm written in IoLanguage

viterbi.io

obs := list("normal", "cold", "dizzy")
states := list("Healthy", "Fever")
start_p := Map with(
    "Healthy", 0.6,
    "Fever", 0.4
)
trans_p := Map with(
    "Healthy", Map with(
        "Healthy", 0.7,
        "Fever", 0.3
    ),
    "Fever", Map with(
        "Healthy", 0.4,
        "Fever", 0.6
    )
)

emit_p := Map with(
    "Healthy", Map with(
        "normal", 0.5,
        "cold", 0.4,
        "dizzy", 0.1
    ),
    "Fever", Map with(
        "normal", 0.1,
        "cold", 0.3,
        "dizzy", 0.6
    )
)

last_states := nil
path := obs map(
    ob,
    last_states = if(last_states,
        states map(
            state, 
            list(state,
                states map(
                    new_state,
                    last_states at(new_state) * trans_p at(state) at(new_state) * emit_p at(new_state) at(ob)
                ) reduce(max)
            )
        ) ,
        states map(state, 
            list(
                state, 
                start_p at(state) * emit_p at(state) at(ob)
            )
        ) 
    ) asMap

    last_states asList reduce(a,b, if(a second > b second, a,b)) first
)

path print