transitions.ts

const SOLID = "SOLID";
const LIQUID = "LIQUID";
const GAS = "GAS";

const transitions = {
    [SOLID]: {
      melt: LIQUID,
      sublimate: GAS,
    },
    [LIQUID]: {
      vaporize: GAS,
      freeze: SOLID,
    },
    [GAS]: {
      condensate: LIQUID,
      deposit: SOLID,
    },
};

function nextTransition(transitions: ???) {
    ...
}