AssocIn.hs

{-# LANGUAGE GADTs #-}

module Lib where

import qualified Data.HashMap.Lazy as M
import Data.Hashable
import Data.Typeable

-- this is what we know about all things from Java
data Val where
  Val :: (Eq a, Hashable a, Typeable a) => a -> Val

instance Hashable Val where
  hashWithSalt salt (Val a) = hashWithSalt salt a

instance Eq Val where
  Val a == Val b =
    case cast b of
      Nothing -> False
      Just bb -> a == bb

examine :: (Typeable a, Hashable a) => Val -> Maybe a
examine (Val a) = cast a

-- simplified, slightly, we won't do variadic inputs
assoc :: Val -> Val -> Val -> Val
assoc map key val =
  case examine map of
    Nothing -> error "not bothering with failure semantics"
    Just mapS -> Val (M.insert key val mapS)

get :: Val -> Val -> Val
get map key =
  case examine map of
    Nothing -> error "not bothering with failure semantics"
    Just mapS -> mapS M.! key

{-

(defn assoc-in
  "Associates a value in a nested associative structure, where ks is a
  sequence of keys and v is the new value and returns a new nested structure.
  If any levels do not exist, hash-maps will be created."
  {:added "1.0"
   :static true}
  [m [k & ks] v]
  (if ks
    (assoc m k (assoc-in (get m k) ks v))
    (assoc m k v)))

-}
assocIn :: Val -> [Val] -> Val -> Val
assocIn _ [] _ = error "more unhandled errors"
assocIn m [k] v = assoc m k v
assocIn m (k:ks) v = assoc m k (assocIn (get m k) ks v)