> On Sep 30, 2017, at 3:14 PM, Didier <[email protected]> wrote:
>
> Is there another way to execute a set of complex steps which does not rely on
> let and can be try/catched in the manner I describe?
I can't emphasize enough the utility of the interceptor chain pattern, as
employed heavily in pedestal.
I use this *everywhere* now. I have code that interleaves interceptors into a
chain to augment them with timing information, audit logs, and more. I have
written code that maps a subset of an interceptor chain over a cluster of
machines, then reduces the results back down locally. Most importantly, they
are fantastically useful when it comes time to debug a complex business process
… you can swap interceptors in and out easily, isolate stateful interceptors to
enable better mocking during tests, and more.
Here's a basic application of interceptors. It's really not much code
considering what you get. This doesn't even scratch the surface of what they
can do.
(ns interceptor.test
(:require
[io.pedestal.interceptor.chain :as chain]))
(def step1
{:name :step1
:enter (fn [ctx]
(let [x "sheep"]
(assoc ctx :result x)))})
(def step2
{:name :step2
:error (fn [ctx ex-info]
(println "so much for step2:" (:exception-type (ex-data ex-info))))
:enter (fn [{:keys [result] :as ctx}]
(println "time to transform" result "into a number")
(update ctx :result #(Long/parseLong %)))})
(defn run []
(chain/execute {} [step1 step2]))
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