Get the field names

[idontgetoutmuch]

This seems useful to me. We could add it to StripFieldNames but then the name doesn't indicate that you can also get the names as well as strip them.

class GetFieldNames (ts :: [(Symbol, Type)]) where
  getNames :: Rec ElField ts -> [String]

instance GetFieldNames '[] where
  getNames _ = []

instance (KnownSymbol s, GetFieldNames ts) => GetFieldNames ('(s, t) ': ts)  where
  getNames _ = symbolVal (Proxy :: Proxy s) : getNames (undefined :: Rec ElField ts)

[acowley]

I think this almost exists in Vinyl. If we had,

rlabels' :: forall f fs. AllFields fs => Rec f fs -> Rec (Const String) fs 
rlabels' _ = rlabels @fs

Then you can do,

ghci> recordToList . rlabels' $ ((#foo =: (23::Int)) :& (#bar =: "hi there") :& RNil)
["foo","bar"]

With extensions FlexibleContexts, TypeApplications, ScopedTypeVariables, and OverloadedLabels.