persistence - Use acid-state like event log in Haskell -


i'm using acid-state in project , quite it. how easy add persistence plain haskell datatypes without boilerplate.

as far understand, acid-state keeps log of events, instead of writing out entire new state on every update. i'm looking way me review log of recent changes state within application, (read-only) list. (something git log, though don't need branching or being able go older commit.)

of course can write own separate log file details of state changes, or model data list of diffs, prefer automatic , allows me use plain datatypes as possible.

is there library similar acid-state, or perhaps internal functionality of acid-state use this?

here's approach ended with:

i using wrapper around data.acid.update (because it's running in monad restricted io) , realized wrapper store event own log. updateevent update constraint implies safecopy update , runput . safeput can serialize bytestring. however... binary representation, not intended humand-readable, , wanted able review it. realized reading acid-state event log disk have same problem.

so added show update constraints of wrapper. @ every place uses state added:

{-# language standalonederiving #-}  ...  $(makeacidic ''state ['update])  deriving instance show update

(standalonederiving might little controversial, not cause problem orphans here, it's in same file.)

in wrapper call show on update , write result own log file. of course loses atomicity of update: possible application crashes between update call , own logging call, i'm willing accept risk.


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