Inferring subtype of custom type

[rupert]

type LatLon = Lat | Lon

type Msg
    = UpdateField LatLon Float
    | ...

Is really just a nested version of:

type Msg
    = UpdateLat Float
    | UpdateLon Float
    | ...

BTW, there is a technique by which data models in Elm can be simplified by math. A custom type behaves like + (plus), and record types behave like * (multiplication).

latlon = lat + lon
msg = latlon * float + x

msg = lat * float + lon * float + x

Mapping Tagged Union types to other languages?

As Math type Content = Text { uuid : String , title : String } | Markdown { uuid : String , markdown : String } | Figure { uuid : String , markdown : String , title : String , imageId : Maybe String } is equivalent to the expression: uuid * title + uuid * markdown + uuid * markdown * title * imageId taking the common factor = uuid * (title + markdown + markdown * title * imageId) Which converted back into Elm gives me an equivalent data model: type alias Content = { uuid : String …