Jeremy Fairbank
@elpapapollo / jfairbank
Build Web Apps
with Elm
Visit README for demo and exercise URLs:
bit.ly/jf-elm-workshop
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Software is broken.
We are here to fix it.
Say hi@testdouble.com
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In beta now!
bit.ly/programming-elm
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Functional and statically typed
programming language for frontend
development
elm
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Web and UI Focused
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Compiles to JavaScript
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No runtime exceptions in
practice.
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The 2nd argument to function `add` is causing a mismatch.
7| add 2 "3"
^^^
Function `add` is expecting the 2nd argument to be:
Int
But it is:
String
Compile time static type checks
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Functional
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Pure Data in
Data out
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Pure No side
effects
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Pure Predictable
and Testable!
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Immutable Data
• Safety and consistency
• Explicit flow of data
• No subtle mutation bugs
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No undefined is not a
function
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Fast
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One framework.
No fatigue.
Update
View
Model
Messages
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✓ Easier to write code
✓ Easier to write tests
✓ Easier to refactor
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Content
• Functions and expressions
• Lists, records, and immutability
• Static types and type aliases
• Union types and pattern matching
• Building Apps with the Elm Architecture
• JSON Decoders
• Adding HTTP to applications
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Format
• Demos via ellie-app.com
• Exercises via ellie-app.com
• Q&A
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Coding Time!
README for demo and exercise URLs:
bit.ly/jf-elm-workshop
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Update
View
Model
Messages
The Elm
Architecture
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Application
State
Model
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Model
Virtual
DOM
View
UI as a Function
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elm
Virtual
DOM
Todo List
Learn Elm
Build awesome Elm apps
Learn functional programming
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×
Todo List
Learn Elm
Build awesome Elm apps
Learn functional programming
User deletes
first todo item
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Todo List
Learn Elm
Build awesome Elm apps
Learn functional programming
View
Model:
New Todo
List
Elm notices missing todo item in virtual DOM list, so it just
removes the corresponding
instead of fully rendering.
elm
Virtual
DOM
×
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Messages
Standardized
application events
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elm
app
model
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elm
app
model
Events
Text Input
Mouse Click
Associate message
with event
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elm
app
model
Events
Text Input
Mouse Click
When event triggers (i.e.
user clicks), deliver
message
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Update
Model
New
Model
Respond to messages and
create new state
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model
Update View
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model
Update View
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model
Update View
VDOM
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model
Update View
VDOM
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model
Update View
Select red color
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model
Update View
Select red color
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model
Update View
Select red color
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model
Update View
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model
Update View
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model
Update View
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model
Update View
VDOM
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model
Update View
VDOM
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Coding Time!
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HTTP
Commands and
Decoders
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elm
app
model
?
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elm
app
model
Commands
HTTP
Dates
Random #’s
Create command with
response message
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elm
app
model
Receive back message with
response value when command
completes
Commands
HTTP
Dates
Random #’s