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@ -176,9 +176,9 @@ marvelous because they move the app forward. Without them,
an app stays stuck in one state forever, never achieving anything. an app stays stuck in one state forever, never achieving anything.
So re-frame embraces the protagonist nature of `effects` - the entire, unruly zoo of them - but So re-frame embraces the protagonist nature of `effects` - the entire, unruly zoo of them - but
it does so in a largely hidden way, and in a manner which is debuggable, auditable, mockable and pluggable. it does so in a controlled and largely hidden way, and in a manner which is debuggable, auditable, mockable and pluggable.
### We're At A Pivot Point ### We're Now At A Pivot Point
The world just changed and, very often, one particular part of it: the **application state**. The world just changed and, very often, one particular part of it: the **application state**.
@ -188,7 +188,7 @@ would an in-memory, central database for the app (details later).
When domino 3 changes this `app state`, it triggers the next part of the cascade When domino 3 changes this `app state`, it triggers the next part of the cascade
involving dominoes 4-5-6. involving dominoes 4-5-6.
### There's a Formula ### There's a Formula For It
The 4-5-6 domino cascade implements the formula made famous by Facebook's ground-breaking React library: The 4-5-6 domino cascade implements the formula made famous by Facebook's ground-breaking React library:
`v = f(s)` `v = f(s)`
@ -198,9 +198,11 @@ A view, `v`, is a function, `f`, of the app state, `s`.
Said another way, there are functions `f` that compute which DOM nodes, `v`, Said another way, there are functions `f` that compute which DOM nodes, `v`,
should be displayed to the user when the application is in a given app state, `s`. should be displayed to the user when the application is in a given app state, `s`.
Or, differently: **over time**, as `s` changes, `f` Or, to capture the dynamics we'd say: **over time**, as `s` changes, `f`
will be re-run each time to compute new `v`, forever keeping `v` up to date with the current `s`. will be re-run each time to compute new `v`, forever keeping `v` up to date with the current `s`.
Or, with yet another emphasis: **over time** what is presented to the user changes in response to application state changes.
In our case, domino 3 changes `s`, the application state, In our case, domino 3 changes `s`, the application state,
and, in response, dominoes 4-5-6 are concerned with re-running `f` to compute the new `v` and, in response, dominoes 4-5-6 are concerned with re-running `f` to compute the new `v`
shown to the user. shown to the user.
@ -262,7 +264,7 @@ which leads, in turn, to an ease in reasoning and debugging.
The two sub-cascades 1-2-3 and 4-5-6 have a similar structure. The two sub-cascades 1-2-3 and 4-5-6 have a similar structure.
In each, it is the second to last domino which In each, it is the second to last domino which
computes "descriptions" of mutations required, and it is computes "data descriptions" of mutations required, and it is
the last domino which does the dirty work and realises these descriptions. the last domino which does the dirty work and realises these descriptions.
In both cases, you don't need to worry yourself about this dirty work. re-frame looks In both cases, you don't need to worry yourself about this dirty work. re-frame looks
@ -316,7 +318,7 @@ registered for handling `:delete-item` `events` like this:
1. a `coeffects` map which contains the current state of the world (including app state) 1. a `coeffects` map which contains the current state of the world (including app state)
2. the `event` 2. the `event`
It returns a map of `effects` - a description `h` returns a map of `effects` - a description
of how the world should be changed by the event. of how the world should be changed by the event.
Here's a sketch (we are at 30,000 feet): Here's a sketch (we are at 30,000 feet):
@ -338,7 +340,7 @@ available by default in the `:db` key.
An `effect handler` (function) actions the `effects` returned by `h`. An `effect handler` (function) actions the `effects` returned by `h`.
Here's what was returned: Here's what `h` returned:
```clj ```clj
{:db (dissoc-in db [:items item-id])} {:db (dissoc-in db [:items item-id])}
``` ```
@ -351,7 +353,7 @@ A key of `:db` means to update the app state with the key's value.
This update of "app state" is a mutative step, facilitated by re-frame This update of "app state" is a mutative step, facilitated by re-frame
which has a built-in `effects handler` for the `:db` effect. which has a built-in `effects handler` for the `:db` effect.
Why the name `:db`? re-frame sees "app state" as something of an in-memory Why the name `:db`? Well, re-frame sees "app state" as something of an in-memory
database. More on that soon. database. More on that soon.
Just to be clear, if `h` had returned: Just to be clear, if `h` had returned: