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> In a rush? You can skip this tutorial page on the first pass. <br>
> It is quite abstract and it will not help you write re-frame code.
> On the other hand, it will considerably deepen your understanding, so
> remember to cycle back to it later.<br>
> In a rush? You can skip this tutorial page on a first pass. <br>
> It is quite abstract and it won't directly help you write re-frame code.
> On the other hand, it will considerably deepen your understanding
> of what re-frame is about, so remember to cycle back and read it later.<br>
> Next page: [Effectful Handlers](EffectfulHandlers.md)
## Mental Model Omnibus
@ -30,22 +30,6 @@ then those patterns will repeat themselves. <br>
> -- Robert Pirsig, Zen and the Art of Motorcycle Maintenance
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## Table Of Contents
- [What is the problem?](#what-is-the-problem)
- [Guiding Philosophy](#guiding-philosophy)
- [It does Event Sourcing](#it-does-event-sourcing)
- [It does a reduce](#it-does-a-reduce)
- [Derived Data All The Way Down](#derived-data-all-the-way-down)
- [It does FSM](#it-does-fsm)
- [Interconnections](#interconnections)
- [Full Stack](#full-stack)
- [What Of This Romance?](#what-of-this-romance)
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## What is the problem?
First, we decided to build our SPA apps with ClojureScript, then we
@ -108,8 +92,8 @@ Sincerely, The Self-appointed President of the Cursor Skeptic's Society.
Every re-frame app will have a different set of `events` and your job is
to design exactly the right ones for any given app you build. These `events`
will be the "language of the system". They'll represent "intent"
(generally the user's). They'll provide the eloquence.
will be the "language of the system". They'll represent "intent" -
generally the user's. They'll provide the eloquence.
And they are data.
@ -146,22 +130,21 @@ Wait. What machine? Well, the Event Handlers you register collectively implemen
the "machine" on which these instructions execute.
In this repo's README, near the top, I explained that re-frame had a
Data Oriented Design. That tends to mean there's a DSL (Domain specific language)
somewhere and an interpreter for it. With re-frame, YOU design a DSL and
then YOU provide the machine to run it.
Data Oriented Design. Typically, that claim means there's a DSL (Domain specific language)
involved and an interpreter for it. As you design your re-frame app,
YOU design a DSL and then YOU provide the machine to execute it.
Summary:
- Events are the assembly language of your app.
- These instructions collectively form a Domain Specific Language (DSL). The language of your system.
- The instructions collectively form a Domain Specific Language (DSL). The language of your system.
- These instructions are data.
- One instruction after another gets executed by your functioning app.
- The Event Handlers you register collectively implement the "machine" on which this DSL executes.
On the subject of DSLs, I'd recommend James Reeves' talk (video): [Transparency through data](https://www.youtube.com/watch?v=zznwKCifC1A)
On the subject of DSLs, watch James Reeves' excellent talk (video): [Transparency through data](https://www.youtube.com/watch?v=zznwKCifC1A)
## It does Event Sourcing
How did that error happen, you puzzle, shaking your head ruefully?
What did the user do immediately prior? What
state was the app in that this event was so problematic?
@ -179,7 +162,7 @@ Note: that's all just data. **Pure, lovely loggable data.**
If you have that data, then you can reproduce the error.
re-frame allows you to time travel, even in a production setting.
Install the "checkpoint" state into `app-db`
To find the bug, install the "checkpoint" state into `app-db`
and then "play forward" through the collection of dispatched events.
The only way the app "moves forwards" is via events. "Replaying events" moves you
@ -216,7 +199,7 @@ Then notice that `reg-event-db` event handlers take two arguments also:
Interesting. That's the same as a `combining function` in a `reduce`!!
So now we can introduce the new mental model: at any point in time,
So, now we can introduce the new mental model: at any point in time,
the value in `app-db` is the result of performing a `reduce` over
the entire `collection` of events dispatched in the app up until
that time. The combining function for this reduce is the set of event handlers.
@ -393,3 +376,8 @@ Next: [Infographic Overview](EventHandlingInfographic.md)
[OM]:https://github.com/swannodette/om
[Hoplon]:http://hoplon.io/
[Pedestal App]:https://github.com/pedestal/pedestal-app
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