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spule
Spule ~ Scottish: [ˈspül] variant of Spool ~ German: [ˈʃpuːlə] Coil, Reel
Introduction: State MGMT and Side-Effects
All too often, state management (MGMT) is an "add-on", an afterthought of a UI/API. However, you may realize by now - if you've spent any significant time using the available MGMT libraries - that state (and coupled effects) is the most infuriating source of complexity and bugs in modern JavaScript apps. Spule aims to be far simpler than the status quo by starting with a simple abstraction over the hardest parts and working outwards to the easier ones.
Getting Started
npm install spule
What if you could compose your app logic on an ad-hoc basis
without creating spagetthi code? Yes, it's possible and one
of the primary goals of spule
At it's core, spule
is async-first. It allows you to write
your code using async
/await
/Promises
in the most
painless and composable way you've ever seen. spule
does
some stream-based
(FRP)
gymnastics under the hood to correograph everything,
however, you won't have to worry about the implementation
details. spule
aims at being approachable to those who
have zero experience with streams. Let's see some examples.
Commands
At the core of spule
is an async spooler (hence the name),
which recieves "Commands" and responds to them. We'll go
into more detail later, but let's jump right in with some
copy/paste examples.
Stupid Command example:
// src/genie.js
import { run$, registerCMD } from "spule"
const GENIE = registerCMD({
sub$: "GENIE",
args: "your wish",
work: x => console.log("🧞♀️:", x, "is my command")
})
// work handler is digested during registration
console.log(GENIE)
// => { sub$: "GENIE", args: "your wish" }
run$.next(GENIE)
//=> 🧞♀️: your wish is my command
registerCMD
takes a config Object
, attaches the work
callback to a pubsub stream for you and returns a Command
Object
that you can use to trigger that callback
(subscription based on the Command sub$
value).
This Object
signature is not only handy as a means to
manage a lot of Commands, but it also avails spule
's
superpower: Tasks
Tasks
Tasks, like Commands, are just data (including Lambdas).
Commands are Object
s and Tasks are Array
s of Commands.
This allows them to be dis/reassembled and reused on an
ad-hoc basis. Let's compose our GENIE
Command with an API
call...
// src/genie.js (continued)
export const GET__FORTUNE = [
// 1st Command args' Object initializes an accumulator
{ args: { api: "http://yerkee.com/api/fortune" } },
// lambda args have access to the accumulation
{
args: ({ api }) => fetch(api).then(r => r.json()),
reso: (acc, { fortune }) => ({ fortune }),
erro: (acc, err) => ({ error: err })
}
]
const FORTUNE__GENIE = [
...GET__FORTUNE,
{ ...GENIE, args: ({ fortune }) => fortune }
]
run$.next(FORTUNE__GENIE)
// => 🧞♀️: Deliver yesterday, code today, think tomorrow. is my command
Logic as Data™
As you can see - within a Task - the only required key on a
Command Object
is the args
key, which provide the
signal-passing functionality between intra-Task Commands.
The only Command that actually does any work
here is
GENIE
(the one with a registered sub$
).
🔍 UTH (Under the Hood): This intra-Task handoff works via an async
reduce
function. AnyObject
returned by a Command is spread into an "accumulator" that can be accessed by any following Commands within a Task (via a unary Lambda in theargs
position).
Hopefully you get a sense of how handy this is already. Have
you ever wished you could pull out and pass around a .then
from one Promise chain to compose with another? Well, now
you - effectively - can. Not only can you recombine Promises
with Tasks, you can also recombine side-effecting code. This
is "Logic as Data"™
And, yes, it gets even better. It may be obvious that you
can de/compose or spread together Tasks (they're just
Array
s). But, what if the shape/signature of your
"Subtask" doesn't match that of the Task that you'd like
spread it into?
Subtasks
// src/zoltar.js
import { run$, registerCMD } from "spule"
import { GET__FORTUNE } from "./genie"
const ZOLTAR = registerCMD({
sub$: "ZOLTAR",
args: { zoltar: "make your wish" },
work: ({ zoltar }) => console.log("🧞♂️:", zoltar)
})
const TOM = registerCMD({
sub$: "TOM",
args: { tom: "👶: I wish I were big" },
work: ({ tom }) => console.log(tom)
})
/**
* use a unary function that takes the accumulator
* Object and returns a Task
*/
const ZOLTAR__X = ({ zoltar }) => [
{ ...TOM, args: { tom: "🧒: I wish I was small again" } },
{ ...ZOLTAR, args: { zoltar } }
]
const BIG__MORAL = [
ZOLTAR,
TOM,
{ ...ZOLTAR, args: { zoltar: "your wish is granted" } },
...GET__FORTUNE,
({ fortune }) => ZOLTAR__X({ zoltar: fortune })
]
run$.next(BIG__MORAL)
//=> 🧞♂️: make your wish
//=> 👶: I wish I were big
//=> 🧞♂️: your wish is granted
//=> 🧒: I wish I was small again
//=> 🧞♂️: Growing old is mandatory; growing up is optional.
Just as using a unary args
function in a Command allows
passing state between Commands, you can use a unary function
within a Task to pass state between Subtasks.
Goodbye 🍝 Code!
This gives new meaning to the term "side-effect" as - in
spule
- side-effects are kept on the side and out of
the guts of your logic. This frees you from the pain that
tight-coupling of state, side-effects and logic entails.
Every feature is strongly decoupled from the others
providing a DX that is versatile, modular and composable.
TODO: IMAGE(s) ♻ Framework Architecture
Command Keys
| Key | Type | Role | Required for |
| ------ | ------ | ------------------------------------------------ | ------------ |
| args
| Any | Command payload/accumulator transforming lambda | always |
| sub$
| String | Pubsub stream topic: connects Command to handler | work
|
| work
| Lambda | dispatch side-effects/state-updates on Command | "work" |
| reso
| Lambda | Promise args
resolution handler | Promises |
| erro
| Lambda | Promise args
rejection handler | Promises |
| src$
| Stream | Upstream/source stream (advanced) | optional |
The SET_STATE
Command (built-in)
TODO
Shorthand Symbols Glossary (spule
surface grammar)
Now that we've seen some examples of Commands and Tasks in use, we'll use a shorthand syntax for describing Task/Command signatures as a compact conveyance when convenient.
| Symbol | Description |
| ------------------- | ----------------------------------------- |
| {C}
| Command Object
|
| {*}
| Object
|
| #
| Primitive value (boolean, string, number) |
| {?}
| Promise |
| {A}
| Accumulator Object
|
| (*) =>
| Lambda with any number of parameters |
| (+) =>
| Non-nullary lambda |
| (1) =>
| Unary lambda |
| (0) =>
| Nullary lambda (aka "thunk") |
| [{C},,]
or [T]
| Task |
| [,,T,,]
or [sT]
| Subtask |
Router
One of the things that can be really frustrating to users of
some frameworks is either the lack of a built-in router or
one that seems tacked-on after the fact. spule
was built
with the router in mind.
spule
provides two routers:
- A DOM router (for clients/SPAs)
- a data-only router (for servers/Node).
🔍 UTH: The DOM router is built on top of the data-only router. Both are implemented as Tasks.
URL = Lens
What is a URL? It's really just a path to a specific resource or collection of resources. Before the glorious age of JavaScript, this - in fact - was the only way you could access the Internet. You typed in a URL, which pointed to some file within a directory stored on a computer at some specific address.
Taking queues from the best parts of functional programming,
spule
's router is really just a
lens
into the application state. As natural as URLs are to remote
resources, this router accesses local memory using
paths
At it's core the spule
router doesn't do very much. It
relies on a JavaScript Map
implementation that retains the
Map
API, but has value
semantics -
rather than identity semantics (aka:
PLOP), which the
native Map
implementation uses - for evaluating equality
of a non-primitive Map
keys (e.g., for Object
/Array
keys).
This - dare I say better - implementation of Map avails something that many are asking for in JS: pattern matching. With pattern matching, we don't have to resort to any non-intuitive/complex/fragile regular expression gymnastics for route matching.
To start, we'll diverge away from the problem at hand for
just a moment look at some of the benefits of a
value-semantic Map
...
Value semantics have so many benefits. As a router, just one. So, how might we apply such a pattern matching solution against the problem of routing?
// src/routes.js
import { EquivMap } from "@thi.ng/associative"
const known = x => ["fortunes", "lessons"].find(y => y === x)
const four04 = [{ chinese: 404, english: 404 }]
const home = [{ chinese: "家", english: "home" }]
const url = "https://fortunecookieapi.herokuapp.com/v1/"
const query = (a, b) =>
fetch(`${url}${a}?limit=1&skip=${b}`).then(r => r.json())
export const match = async path => {
const args = path ? path.split("/") : []
let [api, id] = args
const data =
new EquivMap([
// prevent unneeded requests w/thunks (0)=>
[[], () => home],
[[known(api), id], () => query(api, id)], // guarded match
[[known(api)], () => query(api, 1)] // guarded match
]).get(args) || (() => four04)
// call the thunk to trigger the actual request
const res = await data()
const r = res[0]
return r.message || `${r.chinese}: ${r.english}`
}
const log = console.log
match("fortunes/88").then(log)
// //=> "A handsome shoe often pinches the foot."
match("").then(log)
// //=> "家: home"
match("lessons/4").then(log)
// //=> "请给我一杯/两杯啤酒。: A beer/two beers, please."
match("bloop/21").then(log)
// //=> "404: 404"
If you can see the potential of pattern matching for other problems you may have encountered, you can check out the more detailed section later. We can create pattern-matching guards by using an in situ expression that either returns a "falsy" value or the value itself.
Even if you don't end up using spule
, you may find the
@thi.ng/associative
library very handy!
Now, let's integrate our router. Everything pretty much stays the same, but we'll need to make a few changes to mount our router to the DOM.
// src/routes.js
import { URL2obj } from "@-0/utils"
...
export const match = async path => {
- const args = path ? path.split("/") : [];
+ const args = URL2obj(path).URL_path
let [api, id] = args
const data =
new EquivMap([
[[], () => home],
[[known(api), id], () => query(api, id)],
[[known(api)], () => query(api, 1)]
]).get(args) || (() => four04)
const res = await data()
const r = res[0]
- return r.message || `${r.chinese}: ${r.english}`
+ return {
+ URL_data: r.message || `${r.chinese}: ${r.english}`,
+ }
}
- ...
TODO
It's beyond the scope of this introduction to spule
to
dive into the implementation of our next example. It will
work, but you try it out for yourself on your own (toy)
problem in order to get a feel for it.
UI-first or UI-last?
As you may deduce - if you've gotten this far - is there's a
heavy data-oriented/biased approach taken by spule
. In
fact, we argue that the UI should be informed by the data,
not the other way around.
I.e., start with building out the application state for your various routes and then frame it with a UI. Think of the application state as your information architecture and the UI as your information interior design. While it's possible to start with the design and end with an information architecture, the customer journey can suffer from an over-reliance on "signage" for helping them navigate through the information.
It's not uncommon to start an application/site design with a "site map". Think of this approach like a site map on steroids
Advanced
ADVANCED USE ONLY 👽
HURL tries to hide the stream implentation from the user as
much as possible, but allows you to go further down the
rabbit hole if so desired. You may send Commands to a
separate stream of your own creation during a Task by using
a nullary ("thunk") (0)=>
function signature as the args
value of a Command. If this is the case, the spool assumes
the sub$
key references a stream and sends the return
value of the thunk to that stream This feature can come in
handy for "fire and forget" events (e.g., logging,
analytics, etc.)
import { stream } from "@thi.ng/rstream"
import { map, comp } from "@thi.ng/transducers"
// ad-hoc stream
let login = stream().subscribe(
comp(
map(x => console.log("login ->", x)),
map(({ token }) => loginToMyAuth(token))
)
)
// subtask ({A})=>
let ANALYTICS = ({ token }) => [
{
sub$: login, // <- stream
// thunk custom stream dispatch (0)=>
args: () => ({ token })
}
]
// task
let task = [
// no sub$, just pass data
{ args: { href: "https://my.io/auth" } },
{ sub$: login, args: () => "logging in..." },
{
sub$: "AUTH",
args: ({ href }) => fetch(href).then(r => r.json()),
erro: (acc, err) => ({ sub$: "cancel", args: err }),
reso: (acc, res) => ({ token: res })
},
acc => ANALYTICS(acc),
{ sub$: login, args: () => "log in success" }
]
Stream Architecture:
run$
is the primary event stream exposed to the user via
the ctx
object injected into every hdom
component the
command stream is the only way the user changes anything in
hurl
Marble Diagram
0>- |------c-----------c--[~a~b~a~]-a----c-> : calls
1>- |ps|---1-----------1----------0-1----1-> : run$
2>- |t0|---------a~~b~~~~~~~~~~~a~|--------> : task$
3>- |t1|---c-----------c------------a----c-> : cmd$
4>- ---|ps|c-----a--b--c--------a---a----c-> : out$
Userland Handlers:
a>- ---|ta|------*--------------*---*------> : registerCMD
b>- ---|tb|---------*----------------------> : registerCMD
c>- ---|tc|*-----------*-----------------*-> : registerCMD
Streams
0>-
: userland stream emmissions (run
)1>-
: pubsub forking stream (if emmission has asub$
)2>-
: pubsub =false
? ->task$
stream3>-
: pubsub =true
? ->cmd$
stream4>-
: pubsub emits toregisterCMD
based onsub$
value
work
Handlers
4>-
this is the stream to which the user (and framework) attacheswork
handlers. Handlers receive events they subscribe to as topics based on asub$
key in a Command object.
Built-in Commands/Tasks:
SET_STATE
: Global state update CommandURL__ROUTE
: Routing Task- "FLIP" : F.L.I.P. animations Commands for route/page transitiions
run$
User-land event dispatch stream
This stream is directly exposed to users. Any one-off
Commands next
ed into this stream are sent to the
cmd$
stream. Arrays of Commands (Tasks) are sent to
the task$
stream.
Constants Glossary
| URL component key | description | | ----------------- | -------------------------------------- | | DOM | DOM node target | | URL | full URL/route | | URL_path | route path as array | | URL_domain | top-level domain as array | | URL_subdomain | subdomain as array | | URL_query | node querystring URL2objd URL parameters | | URL_hash | hash string to/from URL if any | | URL_data | data returned by router | | URL_page | page component to render URL_data with |
| router config key | description | | ----------------- | ------------------------------------------------ | | HEAD | metadata wrapper for router (targets DOM ) | | BODY | data wrapper for router | | prep | pre-router behavior Task/Command injection | | post | post=router behavior Task/Command injection | | prefix | URL path string for the router to ignore | | router | @thi.ng/EquivMap pattern matching function |
| Command key (🔎) | description | | ---------------- | ----------------------------------------------- | | sub$ | Command primary/unique key (topic subscription) | | args | signal passing intra-Task Command state value | | reso | Promise resolution handler | | erro | Promise rejection handler | | work | where Commands' actual "work" is done | | src$ | upstream (source stream) Command connector |
| boot
config key | description |
| ----------------- | ------------------------------------------- |
| run | primary userland dispatch function |
| state | global immutable state container |
| root | DOM mount node for application |
| app | root application view |
| trace | enable logging of every global state update |
| draft | state shape scaffolding |
More Pattern Matching
import { EquivMap } from "@thi.ng/associative"
const haiku = args => {
const { a, b, c } = args
const [d] = c || []
const line =
new EquivMap([
[{ a, b }, `${a} are ${b}`],
[{ a, b, c: [d] }, `But ${a} they don't ${b} ${d}`]
]).get(args) || "refrigerator"
console.log(line)
}
haiku({ a: "haikus", b: "easy" })
//=> haikus are easy
haiku({ a: "sometimes", b: "make", c: ["sense"] })
//=> But sometimes they don't make sense
haiku({ b: "butterfly", f: "cherry", a: "blossom" })
//=> refrigerator
We can use any expression in the context of an Object as a
guard. Let's see an example of guarding matches for
Objects
...
let guarded_matcher = args => {
let { a, c } = args
let res =
// for guards on objects use computed properties
new EquivMap([
[{ a, [c > 3 && "c"]: c }, `${c} is greater than 3`],
[{ a, [c < 3 && "c"]: c }, `${c} is less than 3`]
]).get(args) || "no match"
console.log(res)
}
guarded_matcher({ a: "b", c: 2 })
//=> less than 3
guarded_matcher({ a: "b", c: 3 })
//=> no match
guarded_matcher({ a: "b", c: 4 })
//=> greater than 3
- Naming Conventions:
- constants:
CAPITAL_SNAKE_CASE
- generally accepted convention for constants in JS
- used for defining Commands (as though they might cause side effects, their subscription names are constant - i.e., a signal for emphasising this aspect of a Command)
- pure functions:
snake_case
- some novelty here due to pure functions acting like constants in that with the same input they always return the same output
- impure functions:
camelCase
- regular side-effecty JS
- Tasks:
DOUBLE__UNDERSCORE__SNAKE__CASE
- implies the inputs and outputs on either end of a Task
- Tasks also should be treated as pure functions where the output is really just data (and lambdas). This is going in the direction of "code as data"
- constants:
- lots'o'examples
Credits
spule
is built on the @thi.ng/umbrella ecosystem