elixir-JS-elm

all.elm

// Elixir
data = [
  %{ id: 1, value: 0 },
  %{ id: 2, value: 0 },
  %{ id: 3, value: 0 }
]

Enum.map data, fn item ->
  if item.id == 2 do
    %{ item | value: item.value + 1 }
  else
    item
  end
end


// RamdaJs
const data = [
  { id: 1, value: 0 },
  { id: 2, value: 0 },
  { id: 3, value: 0 }
];

const idEq2 = R.propEq("id", 2);

const evolveValue = R.evolve({ value: R.inc });

R.map(R.when(idEq2, evolveValue)) (data);


// Elm
data = [
  { id = 1, value = 0 },
  { id = 2, value = 0 },
  { id = 3, value = 0 }
]

idEq2 = .id >> (==) 2

evolveValue item = { item | value = (+) 1 <| .value <| item }

when predFn projectFn data = if predFn data then projectFn data else data

List.map(when idEq2 evolveValue) data

One should prefer pattern matching:

Enum.map data, fn
  %{id: 2, value: value} = item -> %{item | value: value + 1}
  item -> item
end

or if you want to do nested updates more conveniently:

Enum.map data, fn
  %{id: 2} = item -> update_in item.value, &(&1 + 1)
  item -> item
end

Definitely looks better then the first if/else approach, but still personally I don't find it very reusable. You will always have to defined 2 pattern matchings where one of them actually is just the identity function