In favour of


The Elm language module.

Latest on Hackage:0.13

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BSD-3-Clause licensed by Evan Czaplicki
Maintained by

Elm aims to make client-side web-development more pleasant. It is a statically/strongly typed, functional reactive language to HTML, CSS, and JS. This package provides a library for Elm compilation in Haskell and a compiler executable.




  • Type aliases in port types
  • Add Keyboard.alt and Keyboard.meta
  • Add Debug.crash,, Debug.watchSummary, and Debug.trace
  • Add List.indexedMap and List.filterMap
  • Add
  • Add Basics.negate
  • Add (>>) to Basics as in F#
  • Add –bundle-runtime flag which creates stand-alone Elm programs
  • Error on ambiguious use of imported variables
  • Replace dependency on Pandoc with cheapskate+kate
  • Better architecture for compiler. Uses types to make compilation pipeline safer, setting things up for giving programmatic access to the AST to improve editor and IDE support.

Breaking Changes:

  • Rename (.) to (<<) as in F#
  • Rename to Basics.identity
  • Rename Basics.div to (//)
  • Rename Basics.mod to (%)
  • Remove Maybe.justs for (List.filterMap identity)
  • Remove List.and for (List.foldl (&&) True)
  • Remove List.or for (List.foldl (||) False)
  • Unambiguous syntax for importing ADTs and type aliases
  • sqrt and logBase both only work on Floats now


  • Minor changes to support webgl as a separate library
  • Switch from HSV to HSL
  • Programmatic access to colors with toHsl and toRgb



  • New Array library (thanks entirely to @Xashili)
  • Json.Value can flow through ports
  • Improve speed and stack usage in List library (thanks to @maxsnew)
  • Add Dict.filter and Dict.partition (thanks to @hdgarrood)

Breaking Changes:

  • Revamp Json library, simpler with better names
  • Revamp JavaScript.Experimental library to have slightly better names
  • Remove JavaScript library which was made redundant by ports


Breaking Changes:

  • Overhaul Graphics.Input library (inspired by Spiros Eliopoulos and Jeff Smitts)
  • Overhaul Text library to accomodate new Graphics.Input.Field library and make the API more consistent overall
  • Overhaul Regex library (inspired by Attila Gazso)
  • Change syntax for “import open List” to “import List (..)”
  • Improved JSON format for types generated by elm-doc
  • Remove problematic Mouse.isClicked signal
  • Revise the semantics of keepWhen and dropWhen to only update when the filtered signal changes (thanks Max New and Janis Voigtländer)


  • Add Graphics.Input.Field for customizable text fields
  • Add Trampoline library (thanks to @maxsnew and @timthelion)
  • Add Debug library (inspired by @timthelion)
  • Drastically improved performance on markdown parsing (thanks to @Dandandan)
  • Add Date.fromTime function
  • Use pointer-events to detect hovers on layered elements (thanks to @Xashili)
  • Fix bugs in Bitwise library
  • Fix bug when exporting Maybe values through ports


  • Ports, a new FFI that is more general and much nicer to use
  • Basic compiler tests (thanks to Max New)


  • sort, sortBy, sortWith (thanks to Max Goldstein)
  • elm-repl
  • Bitwise library
  • Regex library
  • Improve Transform2D library (thanks to Michael Søndergaard)


  • Native strings
  • Tango colors
  • custom precedence and associativity for infix operators
  • elm-doc released with new documentation format
  • Realiasing in type errors
  • Rename Matrix2D => Transform2D
  • Add Random.floatList (thank you Max GoldStein)
  • Fix remove function in Dict (thank you Max New)
  • Start using language-ecmascript for JS generation
  • Make compatable with cabal-1.18 (thank you Justin Leitgeb)
  • All functions with 10+ arguments (thanks to Max New)


  • Allow custom precedence and associativity for user-defined infix ops
  • Realias types before printing
  • Switch to Tango color scheme, adding a bunch of nice colors
  • add the greyscale function for easily producing greys
  • Check the type of main
  • Fix miscellaneous bugs in type checker
  • Switch name of Matrix2D to Transform2D


Build Improvements:

  • Major speed improvements to type-checker
  • Type-checker should catch all type errors now
  • Module-level compilation, only re-compile if necessary
  • Import types and type aliases between modules
  • Intermediate files are generated to avoid unneeded recompilation and shorten compile time. These files go in ElmFiles/ by default
  • Generated files are placed in ElmFiles/ by default, replicating the directory structure of your source code.

Error Messages:

  • Cross-module type errors
  • Errors for undefined values
  • Pretty printing of expressions and types


  • Pattern matching on literals
  • Pattern aliases with as (Andrew)
  • Unary negation
  • Triple-quoted multi-line strings
  • Type annotations in let expressions (Andrew)
  • Record Constructors
  • Record type aliases can be closed on the zeroth column
  • (,,) syntax in types
  • Allow infix op definitions without args: (*) = add
  • Unparenthesized if, let, case, lambda at end of binary expressions


  • Build multi-module projects
  • Report all errors in browser


  • Detect hovering over any Element
  • Set alpha of arbitrary forms in collages
  • Switch Text.height to use px instead of em

Bug Fixes:

  • Many bug fixes for collage, especially when rendering Elements.


  • Hot-swapping
  • Much faster page load with pre-compiled Elm files (Max New)

forgot to fill this in again…


  • Add a WebSockets library.
  • Add support for the mathematical looking operator for function composition (U+2218).

forgot to fill this in for a while…


  • Add Dict, Set, and Automaton libraries!

  • Add (,,) notation for creating tuples.

  • Redo HTTP library, allowing any kind of request and more flexibility.

  • Remove the library prefixes Data., Graphics., and Signal. because they were more confusing than helpful.

  • Better type error reporting for ambiguous uses of variables and for variables in aliased modules.

  • Add readInt and readFloat functions.

  • Add complement function to compute complementary colors.

  • Ensure that String is treated as an alias of [Char].

  • Fix bug in pattern parsing. A B _ _ was parsed as A (B _ _).

  • Make pattern matching a bit more compact in generated code.

  • Make generated JS more readable.

  • The Haskell API exports the absolute path to the Elm runtime system (with the corresponding version number). This makes it easier to run Elm programs with less setup.


This version is all about graphics: nicer API with more features and major efficiency improvements. I am really excited about this release!

  • Add native Markdown support. You can now embed markdown directly in .elm files and it is used as an Element. Syntax is [markdown| ... |] where ... is formatted as described here. Content can span multiple lines too.

  • Drastically improve the collage interface. You can now move, rotate, and scale the following forms:

    • Elements (any Element you want can be turned into a Form with toForm)
    • Images
    • Shapes (shapes can be textured now too)
    • Lines This will make it way easier to make games in Elm. Games can now include text, gifs, videos, and any other Element you can think of.
  • Add --minify flag, to minify JS code.

  • Significantly improve performance of pattern matching.

  • Compiler performs beta-reduction in some simple cases.

  • The rendering section of the Elm runtume-system (RTS) has been totally rewritten, making screen refreshes use fewer cycles, less memory, and cause less garbage-collection.


  • Add JSON library.

  • Type-error messages improved. Gives better context for error, making them easier to find. Better messages for runtime errors as well (errors that the type checker cannot find yet).

  • Add Comparable super-type which allows the comparision of any values of type {Int,Float,Char,String}. Now possible to make Set and Map libraries.

  • Parser now handles decimal numbers.

  • Added many new functions for manipulating numbers:

    • truncate, round, floor, ceiling :: Float -> Int
    • toFloat :: Int -> Float
    • (^) :: Number -> Number -> Number
    • e :: Float
  • Foreign import/export statements no longer have to preceed all other variable and datatype definitions. They can be mixed in, making things a bit more readable/natural.

  • Bug fixes:

    • The toText function did not escape strings properly
    • Correct castJSTupleToTupleN family of functions
    • foldr1 took the leftmost element as the base case instead of the rightmost
    • Fix minor display issue in latest version of Chrome.
    • Fix behavior of [ lo .. hi ] syntax (now [4..0] == [], not [0]).


  • Add JavaScript event interface. Allows Elm to import and export JS values and events. This makes it possible to import and export Elements, so users can use JS techniques and libraries if necessary. Conversion between JS and Elm values happens with functions from here: http://localhost:8000/docs/Foreign/JavaScript.elm http://localhost:8000/docs/Foreign/JavaScript/Experimental.elm

  • Add new flags to help with JavaScript event interface.

  • Add three built-in event listeners (elm_title, elm_log, elm_redirect) that make it possible to make some common/simple imperative actions without having to worry about writing the JS yourself. For example: foreign export jsevent “elm_title” title :: Signal JSString will update the page’s title to the current value of the title signal. Empty strings are ignored. “elm_redirect” and “elm_log” events work much the same way, except that “elm_log” does not skip empty strings.

  • Add new Signal functions: count :: Signal a -> Signal Int keepIf :: (a -> Bool) -> a -> Signal a -> Signal a dropIf :: (a -> Bool) -> a -> Signal a -> Signal a keepWhen :: Signal Bool -> a -> Signal a -> Signal a dropWhen :: Signal Bool -> a -> Signal a -> Signal a dropRepeats :: Signal a -> Signal a sampleOn :: Signal a -> Signal b -> Signal b clicks :: Signal () The keep and drop functions make it possible to filter events, which was not possible in prior releases. More documentation:

  • Add examples of JS event interface and new signal functions:

  • Use more compressed format for strings. Should make strings 10-12 times more space efficient than in previous releases. Anecdotal evidence: Elm’s home page is now 70% of its previous size.

  • Add new function to Data.List: last :: [a] -> a

  • Fix parenthesization bug with binary operators.


Major Changes (Read this part!)

  • Add a basic module system.
  • Elm’s JavaScript runtime is now distributed with the elm package. Previously it was available for download as an unversioned JavaScript file (elm-mini.js). It is now installed with the elm compiler as elm-runtime-0.3.0.js. Be sure to serve the Elm runtime system that matches the version of the compiler used to generate JavaScript. When working locally, the compiler will automatically use your local copy of this file.
  • BREAKING CHANGE: rgb and rgba (in the color module) now take their red, green, and blue components as integers between 0 and 255 inclusive.
  • Improve error messages for parse errors and runtime errors.

New Functions and Other Additions

  • Add support for keyboard events: Keyboard.Raw
  • Add buttons in Signal.Input: button :: String -> (Element, Signal Bool)
  • Add new basic element (an empty rectangle, good for adding spaces): rectangle :: Int -> Int -> Element
  • Add (an awkwardly named) way to display right justified text: rightedText
  • Add two basic libraries: Data.Char and Data.Maybe
  • Add some new colors: magenta, yellow, cyan, gray, grey
  • Add functions to Data.List module: take, drop
  • Add functions to Prelude (the default imports): fst, snd, curry, uncurry, and a bunch of list functions
  • Add –make, –separate-js, and –only-js flags to help compile with the new module system.
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