-- Implementation of a mapping, a set of (key,value) pairs.
-- Sergio Antoy
-- Tue Jul 17 08:32:17 PDT 2001
-- updated Thu Jun 29 10:35:40 PDT 2017

-- The store is a list of pairs where the first element is the
-- key and the second is the mapped value.
-- The representation is a list.  If an ordering were available for
-- the keys, a more efficient tree representation would be possible.

-- The initial store is an empty mapping.

-- Getting a mapping fails if and only if the key is not in the store.
-- Consider instead returning a default value, e.g., 0.
-- The value of a key is obtained by instantiating an argument of the call.

-- Setting a mapping either adds a (key,value) pair to the store
-- or updates the value of a key already in the store.
-- Setting a mapping always returns a new mapping.

{-# OPTIONS_CYMAKE -F --pgmF=currypp --optF=defaultrules #-}

init_store = []

get a b (_++[(a,b)]++_) = True

set a b (x++[(a,_)]++y) = x++[(a,b)]++y
set'default a b s = (a,b):s