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Questions tagged [elm]

Elm is a functional programming language for writing web applications that can fully replace, or interoperate with, HTML/CSS/JavaScript.

Elm is a functional programming language that is interoperable with HTML/CSS/JavaScript. It is optimized for creating web UIs, supporting complex user input without using callbacks.

Key features

  • Static types with type inference, with the best compiler errors ever
  • No runtime exceptions
  • No null or undefined in the language
  • Enforces semver for all Elm packages (you must update version number if you make a breaking change)

Resources:

Elm Books

1885 questions
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What does comparable mean in Elm?

I'm having trouble understanding what exactly a comparable is in Elm. Elm seems as confused as I am. On the REPL: > f1 = (<) : comparable -> comparable -> Bool So f1 accepts comparables. > "a" "a" : String > f1 "a" "b" True : Bool So…
Mark Bolusmjak
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Does 'foldp' violate FP's no mutable state principle?

I'm learning about Elm from Seven More Languages in Seven Weeks. The following example confuses me: import Keyboard main = lift asText (foldp (\dir presses -> presses + dir.x) 0 Keyboard.arrows) foldp is defined as: Signal.foldp : (a -> b -> b) ->…
Marcel
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What is the 'msg' in 'HTML msg' in Elm actually?

I'm teaching myself elm and see (of course) many references to Html msg-- I understand that this is a 'parameterised type', that is, that (as I understand it), the constructor of the type Html takes a parameter -- much as List Char does. OK. But…
Cerulean
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Is it possible to iterate over union type in Elm?

I have a type union of colors that I want to render to the user. Is it possible to iterate over all type union values? type Color = Red | Blue | Green | Black colorToStirng color = case color of Red -> "red" Blue -> "blue" …
ondrej
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Is the dollar operator ($) supported in elm?

In Haskell, you can use the $ operator to clean up bits of code, removing the need for parens. Does elm support this operator, or something like it? I can define it myself but I was hoping that this was something built-in. Here's how it…
Conrad.Dean
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How to get query parameters in Elm?

In my Elm program, I'd like to initialize my model based on the query string. For example, if the query string is ?w=3&h=5 I'd like to have: initialModel = { width = 3 , height = 5 } Is that possible to achieve this in Elm, or the only way…
Misha Moroshko
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Concise way of updating a nested value inside a record in Elm (0.18)

I am looking for a concise way of updating a nested value inside a record in Elm (0.18). Given the following example: person = { name = "Steven", address = { country = "Spain", city = "Barcelona" } } I can update person.name to "Steve" using the…
jakubr
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Handling multiple match cases with single statement in Elm

I know in Scala you can handle multiple patterns with a single expression, is something like this possible in Elm? l match { case B(_) | C(_) => "B" }
Max Semikin
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Cmd to simply go to a new webpage in Elm

Is there a way to simply go to a new webpage in Elm, similar to clicking on a link? I have a button that when clicked I want to take the user to another webpage. I know I could make that an a element and use CSS to style it like a button. However,…
at.
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How do I get the current time in Elm 0.17/0.18?

I had asked this question already: How do I get the current time in Elm? And answered it by writing my own (now deprecated) variant of start-app: http://package.elm-lang.org/packages/z5h/time-app/1.0.1 Of course the Elm architecture has since…
Mark Bolusmjak
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Local Storage or other data persistence in elm

I am just beginning to look at Elm with the idea of building a simple web application with it. My idea would require to persist some user data in the browser. Is there a way to handle data persistence directly with Elm? For example in browser…
marcosh
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How to filter out "Nothing" values from Elm Array?

I'd like to define the following function: compactAndConvertToList : Array (Maybe String) -> List String This function should remove all Nothing appearances in the given array, and convert it to List. I came up with the solution below, but it feels…
Misha Moroshko
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Right way to forcibly convert Maybe a to a in Elm, failing clearly for Nothings

Okay, what I really wanted to do is, I have an Array and I want to choose a random element from it. The obvious thing to do is get an integer from a random number generator between 0 and the length minus 1, which I have working already, and then…
betaveros
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Error when convert Http.Error to String with toString in Elm 0.19

I am working on an Elm task to decode the JSON from API. The problem I met is the decoder I've written is not matched the JSON so I want to show the error. But I cannot convert the error message from #Http.Error# type to #String# type in Elm with…
bird
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How to do routing/navigation in Elm without the # (hash) in the URL?

Using the UrlParser.parseHash function i was able to successfully parse the following url: http://localhost:8000/MyRepl.elm/#home/something-else The behavior is as expected, when i copy paste this in the browser and hit enter - the app loads with…
AIon
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