f.hs

lookupDel :: (Eq a) => a -> [(a,b)] -> (b -> [(a, b)] -> t) -> t -> t
lookupDel key as just nothing = go as []
  where
    go ((x,y):xys) ss
      | key == x  =  just y (ss <> xys)
      | otherwise =  go xys ((x,y) : ss)
    go [] ss = nothing


                workMembers :: [IT.TextTree ASpec] -> [(T.Text, Attr)] -> [(Attr, IT.TextTree ASpec)] -> ExM [EncodableAttr]
                workMembers (m:ms) req es = let aspec = IT.rootValue m
                                                member = asNam aspec
                                            in lookupDel member req (\n req' -> workMembers ms req' ((n, m):es))
                                                                    (workMembers ms req es)

                workMembers []    req@(_:_) es = abort (EE_MissingMembers (attrNam [nam]) (fst <$> req))
                workMembers ms@(_:_) []     es = abort (EE_ExtraMembers (attrNam [nam]) (asNam . IT.rootValue <$> ms))
                workMembers []       []     es = traverse (\(attr, subtree') ->
                                                              go (p `dlistSnoc` nam) subtree' attr
                                                          ) es