Thank you for that. I'm curious, when Stuart Sierra mentions a "sequence
monad", does he offer this example simply to keep the Haskell programmers
happy, or is he suggesting that Clojure programmers sometimes use this
pattern? I am especially puzzled by this code that he offers, since this
does not resemble anything that I am familiar with:
(defn chain-consequences [initial-state consequence-fns]
(loop [state initial-state
fs consequense-fns
output []]
(if (seq fs)
(let [events ((first fs) state)
new-state (reduce update-state state events)]
(recur new-state (rest fs) (into output events)))
output)))
On Sunday, May 24, 2015 at 11:11:03 AM UTC-4, tbc++ wrote:
>
> Almost any event-sourcing system is built like this. Datomic is
> (more-or-less) an example of this as it tracks all past transactions and
> keeps indexes that are aggregates of the entire state of the DB.
>
> In addition, Greg Young introduced a event store at CodeMesh 2013 that
> uses this model: https://vimeo.com/84314441
>
> Timothy
>
> On Sat, May 23, 2015 at 10:15 PM, <[email protected] <javascript:>>
> wrote:
>
>> I am watching this video, Stuart Sierra's 2012 talk about Functional
>> Design Patterns:
>>
>> http://www.infoq.com/presentations/Clojure-Design-Patterns
>>
>> His description of event sourcing for functional programming emphasizes:
>> ---- recreate past states
>> ---- recreate any past state by reducing over events
>> ---- just store the inputs
>> ---- cache any intermediate state
>> ---- lost of flexibility
>> ---- every event to the system is a data structure
>> ---- problem: perhaps too many data structures
>>
>>
>> I'm curious where is this pattern actually used?
>>
>>
>>
>>
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>
>
>
> --
> “One of the main causes of the fall of the Roman Empire was that–lacking
> zero–they had no way to indicate successful termination of their C
> programs.”
> (Robert Firth)
>
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