Immediate
main =
Browser.sandbox
{ init = "foo"
, update = \_ m -> String.reverse m
, view = \m -> button [ onClick 0 ] [ text m ]
}
Immediate
> 3 + 5
8 : number
> "Hello!"
"Hello!" : String
Immediate
> x = 3
3 : number
> x + 2
5 : number
Immediate
> double y = y * 2
<function> : number -> number
> double 4
8 : number
Immediate
> sum_of_squares a b = a^2 + b^2
<function> : number -> number -> number
> sum_of_squares 3 4
25 : number
Immediate
type alias Model =
{ x : Float
, y : Float
, centreX : Float
, centreY : Float
}
Immediate
view m =
...
svg
[ width "100"
, height "40"
]
[ ellipse
[ cx "10", cy "34", rx "12", ry "16"
, fill "white", stroke "black", strokeWidth "2px"
] []
...
Immediate
update (MouseChange x y) model =
(
{ model
| x = x
, y = y
}
, Cmd.none
)
Immediate
$ sudo apt-get install nodejs npm
$ sudo npm install -g elm
$ mkdir hello; cd hello
$ echo | elm init
$ echo '
import Html
main = Html.text "Hello"
' > src/Main.elm
$ elm reactor &
$ firefox localhost:8000/src/Main.elm &
Clean
type alias Model =
{ email1 : String
, email2 : String
}
Clean
view model =
...
div
[]
[ button
[ submitDisabled model ]
[ text "Submit" ]
]
...
Clean
submitDisabled model =
disabled
( (validEmail1 model /= Valid)
|| (validEmail2 model /= Valid)
)
Clean
type Msg
= Email1Changed String
| Email2Changed String
update msg model =
case msg of
Email1Changed s ->
{ model | email1 = s }
Email2Changed s ->
{ model | email2 = s }
Clean
- Everything you care about is in the Model
- Everything you see is in view
- Everything that can happen is in update
- No more guesswork
Frustrating
-- TOO MANY ARGS -------------------------------------- src/FrustrationTypes.elm
The `myfn` function expects 1 argument, but it got 2 instead.
10| myfn 3 4
^^^^
Are there any missing commas? Or missing parentheses?
Makefile:8: recipe for target 'type' failed
Frustrating
-- BAD MAIN TYPE ------------------------------------------- src/Frustration.elm
I cannot handle this type of `main` value:
2| main = 1 + 1
^^^^
The type of `main` value I am seeing is:
number
I only know how to handle Html, Svg, and Programs though. Modify `main` to be
one of those types of values!
Frustrating
-- TYPE MISMATCH -------------------------------------------- src/Validation.elm
The 1st argument to `sandbox` is not what I expect:
10| Browser.sandbox
11|> { init = init
12|> , update = update
13|> , view = view
14|> }
This argument is a record of type:
{ init : Model, update : String -> Model -> Model, view : Model -> Html Msg
}
But `sandbox` needs the 1st argument to be:
{ init : Model
, update : String -> Model -> Model
, view : Model -> Html String
}
Frustrating
Success! Compiled 1 module.
Rewarding
Success! Compiled 1 module.
Rewarding
> List.map double (List.range 1 3)
[2,4,6] : List Int
> List.map (\x -> x^2) [1,2,3]
[1,4,9] : List number
Rewarding
> do_twice fn = \x -> fn ( fn x )
<function> : (a -> a) -> a -> a
> do_twice double 4
16 : number
Rewarding
> double_twice = do_twice double
<function> : number -> number
> double_twice 4
16 : number
Rewarding
- Clarity
- Control
- Confidence
- Power
- Happiness!
This work is licensed under a
Creative Commons
