moustache modifier syntax for {{ x | bla }}
suffix .set and .map
moustache modifier {{a, b, c | bla}} = (\a b c ->{a| bla})
moustache modifier maker {{field}} =  (\f a -> {a| field <- f a.field} -- not so sure about this one
up next: moustache modifier without explicit bindings {{ field1 |> f, field2 |> g |> h}} = (\a -> {a| field1 <- f a.field1, field2 <- h (g a.field2)})