mithril 'propMap'

mithril.ts

function propMap<T>(values: Array<[string, T]>): (key: string, value?: T) => T {
    var _prop = (map?: Map<string, T>) => {
      var prop = (key: string, value?: T) => {
        if (value !== undefined) map.set(key, value);
        return map.get(key);
      }
      return prop;
    }

    var map = values.reduce((acc, pair) => {
      acc.set(pair[0], pair[1]);
      return acc;
    }, new Map<string, T>());

    return _prop(map);
  }
}

Example in elm : https://gist.github.com/Warry/b4382a5b4373de57f5ba

propMap : (a -> comparable) -> [a] -> Dict.Dict comparable a
propMap getKey values = Dict.fromList (map (\v -> (getKey v, v)) values)

It allows to check at compile time that key is in T (to make an analogy)

hmmmm. I guess I was mistaken on the purpose of your function! I thought it was transforming an array to map using a property of the object. It looks like it's transforming an array of tuples to a map... My bad.