[erlang-questions] how are implemented lists?

[Richard A. O'Keefe]

On 22/05/2015, at 7:04 pm, Raimo Niskanen <raimo+erlang-questions@REDACTED> wrote:
> 
> 
> Have a look at the brand new map data type.

It's not clear how that would help.
The original request was for

> a fast and concurrent data structure that allows me to retrieve the items
> in order and do pop/tail, while still being abble to remove them by key.

Maps are no more concurrent than lists are.

When requests like this come along, it would be nice to have a
specification that's a bit more precise.  I read this as

typeclass Useful_Key key
  -- at a minimum, support equality, maybe support comparison,
  -- possibly equality and hashing.
data Useful_Key key => Thingy key val

empty :: Thingy key val

add :: key -> val -> Thingy key val -> Thingy key val

remove :: key -> Thingy key val -> Thingy key val

pop :: Thingy key val -> Maybe (key, val, Thingy key val)

so a sort of dictionary/list hybrid.