Another option which allows you to define your own key type is the dependent-map[1] package. It requires implementing some classes for your key type that encode a proof that key equality entails equality of the type indices. If the documentation is insufficient feel free to ask me for more details or examples.
[1] http://hackage.haskell.org/package/dependent-map On Jul 31, 2012, at 6:56 AM, Alexander Foremny <alexanderfore...@gmail.com> wrote: > At first glance I noticed some problems with the vault library for my > particular approach. > > Despite from being unique, Key values don't appear to carry any > information like the Label I need. However, it might be possible to > work around that. > > The more grave problem seems to be that a Key cannot be > (de-)serialized. This might be impossible due to the type parameter a > in Key a. > However, it is no problem to fix the types of values to some finite > collection. > > Because of this some solution built around Dynamic seems to be more > and more appropriate. But I'll try to investigate vault further. > > Regards, > Alexander Foremny > > 2012/7/31 Alexander Foremny <alexanderfore...@gmail.com>: >> Dear Michael, >> >> thank you very much for your quick and interesting response. This >> looks very much like what I want! >> >> Regards, >> Alexander Foremny >> >> 2012/7/31 Michael Snoyman <mich...@snoyman.com>: >>> On Tue, Jul 31, 2012 at 1:13 PM, Alexander Foremny >>> <alexanderfore...@gmail.com> wrote: >>>> Hello list, >>>> >>>> I am currently thinking that a problem of mine would best be solved if >>>> there was a Map-like data structure in which the value returned is >>>> parametrized over the lookup type. >>>> >>>> I wonder is this makes sense and if such a data structure exists or if >>>> it could be created while still being well typed. I essentially want >>>> to statically define a scope of Key values and dynamically define a >>>> list of keys. >>>> >>>>> -- Scope of possible keys. >>>>> type Label = String >>>>> data Key a where >>>>> KeyStr :: Label -> Key String >>>>> KeyInt :: Label -> Key Int >>>>> KeyChoice :: Label -> [a] -> Key a >>>> >>>>> -- Some key values, to be extended at runtime. >>>>> strKey "Some String" >>>>> strKey' "Another String" >>>>> intKey "Some integer" >>>>> choiceKey "Chose one" [ "a", "b", "c" ] :: KeyChoice String >>>> >>>> Now I need a data structure to possibly associate a value to the key. >>>> >>>>> data MapG = ... >>>>> type Value a = a >>>>> insert :: Key a -> Value a -> MapG Key Value -> MapG Key Value >>>>> lookup :: Key a -> MapG Key Value -> Maybe (Value a) >>>> >>>> I tried implementing this with multiple Map k a's. I tried adding a >>>> phantom type on some storage type of to implement KeyChoice as of type >>>> Key Int, but I ran into troubles with this approach. I wonder if >>>> Dynamic or Type Families could achieve this, but I am quite at a loss >>>> and would like to hear your opinion. >>>> >>>> I did try to search for this a bit, but I don't quite know how to >>>> phrase my problem. I'd like to apologize in advance if this question >>>> has been asked already. >>>> >>>> Regards, >>>> Alexander Foremny >>>> >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe@haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> I think you might be looking for something like vault[1]. >>> >>> HTH, >>> Michael >>> >>> [1] http://hackage.haskell.org/package/vault > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
