Composable Web UIs in Julia



Build Status

This package is beta quality and has a large surface area for bugs. Do not use it for anything important.

A web server for 2016. Escher's built-in web server allows you to create interactive Julia UIs with very little code. It takes care of messaging between Julia and the browser under-the-hood. It can also hot-load code: you can see your UI evolve as you save your changes to it.

Escher provides an easy to use rich functional library of UI components: the built-in library functions support Markdown, Signal widgets, TeX-style Layouts, Styling, TeX, Code, Behaviors, Tabs, Menus, Slideshows, Plots (via Gadfly, Vega, VegaLite) and Vector Graphics (via Compose) – everything a Julia programmer would need to effectively visualize data or to create user-facing GUIs. The API comprehensively covers features from HTML and CSS, and also provides advanced features. Its user merely needs to know how to write code in Julia.

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In a Julia REPL, run:


You might want to link escher executable ~/.julia/vX.Y/Escher/bin/escher to /usr/local/bin or somewhere in your PATH, especially if you want to start Escher Server from the CLI:

$ ln -s ~/.julia/v0.4/Escher/bin/escher /usr/local/bin/

2. Usage

2.1. Start the server

The Escher server will start a web server on port 5555 (default).

a. From the terminal /CLI

Go to a directory from which you want to serve Escher UI files. You can start with the examples folder.

$ cd 
$ /escher --serve

Escher comes with a few example files, you may use them to learn more about the framework. The examples are located in the examples/ folder in the julia Escher package folder, usually ~/.julia/vX.Y/Escher/examples.

b. From the Julia REPL

Load the Escher package and serve.jl file.

julia> using Escher
julia> include(Pkg.dir("Escher", "src", "cli", "serve.jl"))

Move to a directory from which you want to serve Escher UI files.

julia> cd(Pkg.dir("Escher", "examples"))

Note: Example files which include plots, such as plotting.jl, also require the Gadfly and ComposeDiff packages to be installed.

julia> Pkg.add("Gadfly")
julia> Pkg.add("ComposeDiff")

Start the Escher Server.

julia> escher_serve()

2.2. Load UI

Visit http://localhost:5555/<file-name.jl> to see the output.

Please Note:

  • if you leave out the file name it will default to index.jl.
  • files containing plots may take a while to load the first time you visit them.
  • if you run Escher in a virtual machine or container environment, you may need to adjust the local host address.

3. Escher UI file format

The most basic Julia Escher UI file may be summed up as below:

# user outer_code

function main(window)

  # user inner_code



  • user outer_code should contain code required to generate and support the UI (using, import, function definitions etc.).
  • the main function definition is required and must take a window argument, even if it may not use it.
  • the window object contains some information about the current browser window. Specifically, window.assets is an input signal which can be used to load HTML dependencies on-the-fly. window.alive is a boolean signal that tells you if the window is still open. window.dimension is a 2-tuple representing the current size of the window in pixels.
  • user inner_code should contain code needed for rendering. Such code may be pushing HTML assets to window.assets and preparing the content and layout, explained in the UI Build Guide.
  • as with any Julia function, if return keyword is missing, the last expression is returned.
  • the returned UI_expression is the one used to generate the UI, so everything you need to render needs to be inside it. One can build complex webpages using the layouts API to package the content, explained in the UI Build Guide.

When your files get complicated, or you like to follow protocol, you may need to break the code into sections. Escher is inspired by Elm language and borrows its file pattern:

  • Model : the state af your application
  • Update : a way to update your state
  • View : a way to view your state as HTML

With this pattern in mind, the extended general UI Escher file looks like this:

# using, import, include statements

### Model ###
# declare functions to build your application's state
# declare types and instantiate variables to hold model data

### Update ###
# declare functions to update the state
# declare types and instantiate variables to hold update data

### View ###
# declare functions to display the state
# declare types and instantiate variables to hold view data

function main(window)
  # maybe some code

4. UI Build Guide

4.1. Escher foundation

Escher functionality is based on the Web Components Standard. The key facility of the Web Components spec is that it gives developers the ability to create their own custom HTML elements which can have pre-defined behavior which can interact with its parent / sibling / child elements.

Web Components consists of several separate technologies. You can think of Web Components as reusable user interface widgets that are created using open Web technology. They are part of the browser, and so they do not need external libraries like jQuery or Dojo. An existing Web Component can be used without writing code, simply by adding an import statement to an HTML page. Web Components use new or still-developing standard browser capabilities.

A short explanation (for detailed explanation visit the links) of the technologies used is:

  • one can create Custom HTML Elements to run in the Browser natively without other dependencies.
  • Custom Elements are created from HTML Templates.
  • Templates must be loaded /imported in the webpage, once per page, to provide de source code for Created Elements.
  • the webpages are stored on the Browser in a data structure called the Document Object Model, or DOM
  • to make the interaction between the server and the browser more efficient, a copy of the DOM is saved on the server, in what is called a Local /Shadow /Virtual DOM, and only the changes are sent to the browser.

In Escher's case, the UI starts out as a UI_expression Tile object, then gets converted /rendered to a Patchwork.jl Elem object in the Virtual DOM, and then, the changes are sent over the network to the Browser as JSON, where it gets rendered as the DOM.

UI_expression Escher.Tile -> Patchwork.Elem -> DOM

The Escher Tile objects are bound to HTML templates. These templates consist of both custom HTML elements as well as off-the-shelf Polymer elements. All HTML Templates are stored inside the assets/ folder in Escher. Basic elements are loaded by default, like Signal signals.html, Behavior behavior.html and other basic third party custom element libraries (including some Polymer).

HTML Templates for dependencies which are not always required (Widgets widgets.html, CodeMirror codemirror.html, TeX tex.html etc.) are also stored in the assets/ folder, but the user has to load them specifically:

  • multiple templates may be defined in the same HTML file.
  • if the template required is inside an templates.html file, the user can call push!(window.assets, "templates") to load that file as an HTML import. Please notice that only the filename "templates", no extension, is used in the method call.
  • the push! method is called once per file, inside the main function, usually as the first lines in the user inner_code.

For your reference, the default HTML content of the assets/ folder is listed below:

no HTML file content API loading-time
1 animations.html HTML animations elements - user
2 basics.html imported by every Escher page implicitly. It loads Polymer, escherd.html, signals.html, behavior.html and the default stylesheets, in that order. - auto
3 behaviour.html contains custom elements used to set up the most basic event handlers, such as clickable-behavior, keypress-behavior, watch-state (fired when some attribute of the parent changes). Behavior auto
4 camera.html camera widget custom element - user
5 codemirror.html codemirror HTML element Widgets user
6 date.html datepicker HTML element Widgets user
7 escherd.html it sets up the communications with the browser side code - auto
8 icons.html icon and icon button elements Higher Order Layouts user
9 layout2.html advanced layout elements like menus, tabs, pages etc. Higher Order Layouts user
10 signals.html the elements here correspond to those rendered by basics/signal.jl signal-transport element, which is used to annotate that another element would like to send some events to the server. Signal auto
11 tex.html TeX/LaTeX element TeX user
12 widgets.html interactive HTML elements like buttons, text input etc. Widgets user

For detailed information, not required for general use, please read the Browser-Side Section of this documentation.

4.2. Escher Basics

4.2.1. Escher Tile type

Escher introduces the Julia abstract immutable type Tile. Every renderable UI element is a subtype of Tile. The return expression of the function main(), named UI_expression in chapter 3, is a Tile.

The Escher Type tree looks something like this:

Tile :> Concrete_Subtypes
     :> Behavior :> Concrete_Subtypes
                 :> Widget :> Concrete_Subtypes
                           :> Selection :> Concrete_Subtypes
     :> Flex Container :> Concrete_Subtypes

You can navigate the Type tree using the Julia super(Type) and subtypes(Type), or, if you want a detailed overview, use the function below. The code was taken from the Julia Wikibooks page.

level = 0
function showtypetree(subtype)
    global level
    subtypelist = filter(asubtype -> asubtype != Any, subtypes(subtype))
    if length(subtypelist) > 0
         println("\t" ^ level, subtype)
         level += 1
         map(showtypetree, subtypelist)
         level -= 1
         println("\t" ^ level, subtype)

Run the function on the Tile type to get a detailed overview.

julia> showtypetree(Tile)

4.2.2. Escher Tile types use cases

A Tile is the basic currency in Escher. Most of the functions in the Escher API take Tiles, among other things, as arguments, and return a Tile as the result. Tiles are immutable, once created there is no way to mutate them. When a function is said to be called on a Tile it actually returns a new Tile with the new characteristics.

A Behavior is a Tile that can result in a stream of values. The stream of values can be given intents, put into signals, used to trigger updates from other behaviors. See subscribe, intent, sampler and capture in the Signal API.

A Widget is an abstract Subtype of Behavior. It is used to create interactive Tiles.

An Intent is a transformation applied to the stream of values coming from a Behavior Tile. The purpose of an Intent is to turn Widget messages into types in the business logic of the application, JSON messages into appropriate values. Attaching an Intent to a Behavior results in a new Behavior. A Widget or a Behavior has a default Intent defined by the default_intent generic function. When another Intent is attached to a Behavior, it gets chained to the default Intent.

A Selection is an abstract Subtype of Widget used to represent elements like DropdownMenu, Menu, Pages, SlideShow, SubMenu or Tabs.

Flex Container is a special Tile that can stretch or contract inside its context based on set rules.

4.2.3. Create Tiles Create Empty Tile

A special kind of Tile is the Escher.Empty, a concrete subtype of Escher.Tile type. It can be created using the empty keyword. The following example code will create an empty "orange" Tile with the size of 10em x 10em:

Example 1: Empty tile

function main(window)
    fillcolor("orange", size(10em, 10em, empty))


Empty Tile Output

A second kind of empty tiles are created with the hline and vline functions, from the Embellishment API. These are used to create horizontal and vertical lines, and they return bordered tiles of height or width 0. Create Text Tiles

Functions that can take textual arguments and return a Tile are found in the Typography API. Some of these functions are plaintext, heading, h1, h2, h3, h4, title, blockquote and code. For detailed information, please see the documentation.

Example 2: Text tile

function main(window)
    plaintext("Hello, World!")


Hello World! Other Content Tiles

Other kind of content can be created using the list, image, link and abbr functions. Detailed information is available in the Content API. Create Markdown Tiles

A special case for creating tiles is the Markdown tile. The md"" string macro can generate markdown tiles from a markdown string.

Example 3: Markdown tile

function main(window)
**Things to do:**

- Create *universe*
- Make a *pie*


Things to do:

  • Create universe
  • Make a pie Create TeX Tiles

Escher can create TeX Tiles from TeX objects using the tex(text::LaTeXString). TeX asset is not loaded by default.

To create a LaTeX string there are two options:

  • use the L" ", and L""" """ for multi-line text, macro.
  • use the latexstring(args...) function.

The latexstring(args...) works in similar fashion to string(args...), supports string interpolation, but the arguments are required to have escaped characters (\ and $ become \ and \$). For more information about the LaTeXString type read here.

Example 4: TeX tile from macro

function main(window)
    push!(window.assets, "tex")

    tex(L"f(x) = \int_{-\infty}^\infty \hat f(\xi)\,e^{2 \pi i \xi x} \,d\xi")


TeX Tile Output

Example 5: TeX tile from function

function main(window)
    push!(window.assets, "tex")

    a = "f(x) = \\int_{-\\infty}^\\infty \\hat"
    b = "f(\\xi)\\,e^{2 \\pi i \\xi x} \\,d\\xi"

    tex(latexstring(a, " ",b))


TeX Tile Output Create Plot Tiles

Gadfly plots are essentially immutable values too. Escher type-casts Gadfly plots to tiles. Gadfly module is not loaded by default, it may take a while to load for the first time.

Example 6: Gadfly Plot tile

using Gadfly

function main(window)
    plot(z=(x,y) -> x*exp(-(x-int(x))^2-y^2),
        x=linspace(-8,8,150), y=linspace(-2,2,150), Geom.contour)


Gadfly Tile Output Create Vector Graphics

Compose graphics work the same way as Gadfly plots. Compose and Color madules are not loaded by default.

Example 7: Compose Vector Graphics tile

using Compose
using Colors

# define the `sierpinski` triangle function
function sierpinski(n)
    if n == 0
        compose(context(), polygon([(1,1), (0,1), (1/2, 0)]))
        t = sierpinski(n - 1)
                (context(1/4,   0, 1/2, 1/2), t),
                (context(  0, 1/2, 1/2, 1/2), t),
                (context(1/2, 1/2, 1/2, 1/2), t))

main(window) = compose(sierpinski(6))

The last line from previous example is a shorthand notation to the following code:

function main(window)


Compose Tile Output Converting other Types to Tile

If, instead of Tile, other type of value is used, Escher will try to convert it to one. One such examples is using textual data, like String. The next line of code is valid and will return a "pink" Tile with the content "Simple text" and a 1em padding. Please note that Compose package exports its own version of pad function. For this reason it is required that you use Escher.pad.

Example 8: Convert other tiles

function main(window)
    fillcolor("pink", Escher.pad(1em, "Simple text"))


Text Tile Output

4.2.4. Customize Tiles

Tiles are immutable, when a function is said to modify a Tile, it instead returns a different Tile with the required specifications.

For the text tiles, there are some specific functions that apply to text, like fontsize, fontfamily, fontcolor etc., in the Typography API.

For general Tile use, like border, bordercolor, borderwidth etc., you can use the Embellishment API.

4.2.5. Layouts Basic Layouts

Escher provides primitives like hbox, vbox, hskip, vskip, and flex for laying out tiles into grids. Complex layouts can be composed from smaller parts. For detailed information, please read the Guide and the Layout API.

Example 9: Basic Layout

a,b,c,d = map(fillcolor, ["#837", "#859", "#892", "#875"],
    map(Escher.pad([left, right], 1em), ["A", "B", "C", "D"]))

function main(window)
    x = vbox(a, b, c, d)
    y = vbox(d, c, b, a)

    hbox(x, y)

x and y are vertical arrangements of 4 tiles each, these arrangements are themselves put in a hbox to place x next to y.


Basic Layout Tile Output Higher Order Layouts

The Higher Order Layout API provides ready-to-use interactive Tiles like tabs, pages, menus etc.

Example 10: Higher Order Layout

using Compose, Gadfly, Colors

# define the sierpinski function, see Example 7

function main(window)
    # load assets
    push!(window.assets, "layout2")

    # create the tabs
    tabbar = tabs([
         hbox("Tab 1"),
         hbox("Tab 2"),
         hbox("Tab 3"),


    # create the pages
    tabcontent = pages([
        plot([sin, cos], 0, 25),
        title(3, "web component all the things"),

    # connect the tabs to pages
    # returns a pair of "connected" tab set and pages
    t, p = wire(tabbar, tabcontent, :tab_channel, :selected)

    # stack them on top of each other
    vbox(t, p)

The pages function combines tiles into a set of pages - only a single page is visible at a time. Pages can be combined with tabs to allow switching between pages.


HO Layout Tile Output

A special case is the Slideshow API, used in presentations to create Julia slideshows.

Another useful feature is the class function found in the Utils API.

4.2.6. Syntax simplification

While it is possible to chain function calls to obtain the desired result, it quickly becomes cumbersome. Fear not, Escher functions have curried methods: omitting the last Tile argument to Escher functions returns a 1-argument function that takes a Tile argument.

f(arguments, Tile) = f(arguments)(Tile) = Tile |> f(arguments)

For example, Escher.pad(10mm) returns an anonymous function of 1 argument which must be a Tile, and that returns a new Tile with the specified 10mm of padding. Therefore, Escher.pad(10mm, txt) is equivalent to Escher.pad(10mm)(txt) or txt |> Escher.pad(10mm). This is helpful when you want to apply, for example, the same padding to a all the tiles in a vector. e.g. map(Escher.pad(10mm), [tile1, tile2]) will return a vector of two tiles with 10mm padding each.

Moreover, using the curried version with the |> infix operator makes for code that reads better.

4.2.7. Interactive UI

Reactive.jl package allows "reactive programming" in Julia. Reactive programming is a style of event-driven programming based on signals. A signal is a change/update in a data value which can also be linked/associated with a UI object/widget, asset, to form a UI Signal which is triggered by event and/or change in state of a UI. A UI is not required to use the Signal Communication paradigm. A UI Signal is a specific case of Signaling communication, it is a Signal which is associated with a UI Object/Widget. Reactive.jl's documentation provides an overview of the Signal framework. At this point it is highly recommended that you read it. Also, you should read the Escher Signal API.

There are two facets to this rule:

  • Getting the input from tiles
  • Creating a UI Signal(s) by associating a UI object/widget (asset) with a signal(s)

In practice, the main function might take the form below. We have used two Signals and two Assets to illustrate how they work together.

function main(window)
    # load "assets" HTML code, for example "widgets" or "tex"
    push!(window.assets, "assets")

    # create signals to hold your assets value, with an initial value
    # Signal can also be typed: Signal{Type}()
    input_signal_1 = Signal("initial_value_1")
    input_signal_2 = Signal("initial_value_2")

    # link the interactive assets to the input signals to create linked assets,
    # for example a `slider` or a `textinput` widget
    linked_asset_1 = subscribe(input_signal_1, asset_1)
    linked_asset_2 = subscribe(input_signal_2, asset_2)

    # create a Signal of UI as a return UI_expression
    # output_signal = Signal(UI_function(input_signal)) = map(UI_function, input_signal)
    # return UI_expression that includes linked widgets and passes input signals as arguments
    # in this example `vbox` was used to group the two assets in one `Tile`, but it can also be `hbox`
      map(linked_asset_1, input_signal_1),
      map(linked_asset_2, input_signal_2)

Please note that:

  • the map function can be replaced with the Do-Block Syntax and will become: map(input_signal) do args # function_body # return UI_expression that includes linked_widget end
  • multiple Signals and normal variables can be used and passed as arguments to the UI_function.
  • the UI expression vbox(map(asset_1, signal_1), map(asset_2, signal_2)) can also be expressed as: map(signal_1, signal_2) do args vbox( asset_1, asset_2 ) end
  • args can be replaced with _ character, in case you don't need to use the Signal value in the UI. One such example is the Button widget, if the user only requires it to fire an action. Creating a signal of UI using these signals

Some Tiles (particularly those that are subtypes of Behavior which is in turn a subtype of Tile) can write to Reactive's Signal signals. Widgets such as sliders, buttons, dropdown menus are subtypes of Behavior. The function subscribe lets you pipe updates from a behavior into a signal.

Example 11: Interactive Tiles

function main(window)
    # load assets, in this case "widgets"
    push!(window.assets, "widgets")

    # create a Signal which holds the angle at any given time
    iterations = Signal(0)

    # create a Signal of UI as a return UI_expression
    # in this simple case, the liked_signal is passed as a UI_expression
    connected_slider = subscribe(iterations, slider(0:7))

The connected_slider renders as a slider and updates the signal iterations when the slider's knob is moved by the user.


Interactive Tile 1 Output Getting the input from tiles

Let's now use the iterations Signal to show an interactive Sierpinski's triangle.

Example 12: Interactive UI

using Compose, Colors

# define the sierpinski function, see Example 7

function main(window)
    # Load HTML dependencies related to the slider
    push!(window.assets, "widgets")

     # create a Signal which holds the number of iterations to show
     # the starting value is 5
    iterations = Signal(5)

     # link a widget to the iterations Signal to create a connected_slider
    connected_slider = subscribe(iterations, slider(0:7, value=5))

    # create a Signal of UI as a return UI_expression
    map(iterations) do n


Interactive Tile 2 Output Interactive Tiles

Escher provides ready-to-use Tiles like buttons, input, codemirror etc., in the Widgets API. Keep in mind that, regular and interactive, Tiles can be augmented with clickable, selectable, keypress etc. behavior via the Behavior API.

4.3. Escher Advanced

This section is intended to provide a more detailed view on the way Escher works and how to create your own custom Tiles.

4.3.1. Custom Tiles

I can think of three reasons why one might need to create custom Tiles, for fun not included:

  • if the current APIs do not provide the elements you require, you can build your own.
  • Escher may not give access to all available properties defined in the HTML element, or it may have certain default values that you would like to change.
  • you might want to optimize your code. When loading assets, all templates in the assets package get loaded into the webpage, even the ones that are not used. For the development phase this is not an issue, but in production you might want to provide a faster loading time by creating your package only with the templates you are using.

To create a new custom Tile you need three things:

  1. a custom HTML element you wish to use
  2. a Tile which corresponds to the custom element. The Tile fields do not necessarily mirror the properties of the HTML.
  3. a render(::myTile, state) which returns an Elem, which in turn creates the the same custom HTML element mentioned in step 1.

These three requirements are placed in two different files:

  1. assets/<asset-name>.html is where you place the HTML code
  2. src/library/<asset-name>.jl holds the custom Tile and the render definition

Assets files, both .html and .jl, can contain multiple custom element definitions.

For usage, the <asset-name>.html is pushed to the browser from the main function inside your Julia Escher UI file: push!(window.assets, "asset-name").

On the other hand, <asset-name>.jl must be imported in the src/Escher.jl file: include("library/<asset-name>.jl"). A restart of Escher server is necessary in order to recompile with the new addition.

4.3.2. HTML code

This section is intended to show how to use custom HTML elements, not to create ones. For creating HTML elements please see the Polymer guide. Custom HTML elements format

The format for custom element templates is shown below. The custom element name is custom-element. All custom elements must have multi-word names, separated by the "-" (dash) character. This code does not render, it is only a template /definition, like a Julia function definition, in this regard.



Usually the template code is kept in a separate file, <custom-element>.html and imported into the main file using the link rel="import" element. Custom HTML elements sets

Multiple elements may be grouped in a set or <templates-file>.html.

The templates file is imported in similar fashion to the custom element import: Escher custom HTML elements library

Escher makes use of some of the Polymer Library elements. The Polymer library is installed and managed by bower. It is stored locally in assets/bower_components/, so references are made with relative path:

Using the Polymer Library has some advantages: you do not need to tinker with the HTML /JS code, each provided element has an exposed API and you only need to address the properties /methods /events you are interested in, provided that it is enough to have a functional element. The content of the asset .html file

In conclusion, inside your assets/<asset-name>.html file, depending on your needs, you might have one of these choices:

  1. a one element definition of the custom HTML element, like the assets/tex.html.
  2. a list of one element imports of the custom HTML element, like the assets/widgets.html
  3. a list of one or more one element or sets imports, like the assets/icons.html.

4.3.3. Julia code

For each template, we need to create a Tile definition, plus methods, and the corresponding render method. They are both placed in the same file, one after the other. Creating new Tile types

The Tile type in Julia is created using the @api macro. This lets Escher use a high-level DSL for defining the API for a Tile type. Think of it as defining methods for the constructors of the type with a system more powerful than plain dispatch definitions.

Here is the syntax of @api:

@api  => (  <: Tile) begin
   # one or more

This expression generates a type whose name is <TypeName>, while the constructor itself will be named <constructor_name>. The convention in Escher is to use lower cased names for the actual constructors and CamelCased names for the types.

A doc(md"<doc string>") expression defines the documentation of a Tile constructor. The <arg_specifics> takes a keyword argument doc="" which can define the documentation of each argument (e.g. arg(color::Color, doc="border color."). This is what gets used while generating the API documentation at escher-jl.org.

The fields are defined by one or more <arg_specifics>. The annotation also includes information about how the filed works. The type of arguments are as follows:

  • arg(x::SomeType)
    • it becomes x::Any in all method signatures, argument will be converted to SomeType before construction.
    • it means for the caller that it's a normal argument. the value gets converted to the right type if it can be.
  • arg(x::SomeType=default_value)
    • results in two kinds of method signatures, one with x::Any, argument will be converted to SomeType before construction; the other is without x in the list of arguments, the constructor then uses the default value in its place.
    • it means the argument is not required, if it's missing the default value is used. It's similar to Julia's trailing optional arguments, but it can appear in the beginning of an argument list too.
  • kwarg(x::SomeType=default_value)
    • it becomes x=default_value (kwarg) in all method definitions, argument will be converted to SomeType.
    • it means it's a regular old keyword argument. the value gets converted to the right type if it can be.
  • typedarg(x::SomeType)
    • becomes x::SomeType in all method signatures
    • it means the argument is required and must be a SubType instance.
  • typedarg(x::SomeType=default_value)
    • results in two kinds of method signatures, one with x::SomeType; the other without x in the list of arguments, the constructor then uses the default value in its place.
  • typedkwarg(x::SomeType=default_value)
    • becomes x::SomeType=default_value (kwarg) in all method definitions.
    • means a keyword argument which must be a SomeType instance
  • curry(x::SomeType)
    • results in the creation of two kinds of methods. One which has the argument x::SomeType in its signature, another that does not have an argument in its place. The latter method returns a lambda that takes x and calls the former method to actually construct the type.
    • means if this argument is missing, then you get back a lambda which you can call with the missing argument. Usually only the last non-keyword argument, if any, is created with curry. This makes |> convenient to use in many cases. This argument encourages a free-flowing experimental style. You can more easily write <a long expression> |> x than x(<a long expression>), handy while playing with changes, sometimes |> reads better.

Example 13: @api macro usage

@api border => (Bordered <: Tile) begin

Generated definitions

border(side::Any, tile::Any; color=colorant"black", thickness::Length=1pt) = Bordered(side, convert(Tile, tile), convert(Color, color), thickness)
border(side::Any; color=colorant"black", thickness::Length=1pt) = tile -> Bordered(side, tile, convert(Color, color), thickness)

The Tile argument is the object that will be getting the border in this case. This is a general style in Julia, you construct new tiles to endow some property to an input tile.

The user can call it in two different ways:

border(side, tile, color=my_color, thickness=2pt)
tile |> border(side, color=my_color, thickness=2pt)

Example 14: @api macro usage

@api border => (Bordered <: Tile) begin

Generated definitions

border(style::Any, side::Array{Side}, tile::Any; color=colorant"black", thickness::Length=1pt) =
    Bordered(convert(BorderStyle, style), side, convert(Tile, tile), convert(Color, color), thickness)

border(style::Any; color=colorant"black", thickness::Length=1pt) =
    Bordered(convert(BorderStyle, style), [left,right,top,bottom], tile, convert(Color, color), thickness)

border(style::Any, side::Array{Side}; color=colorant"black", thickness::Length=1pt) =
    Bordered(convert(BorderStyle, style), side, tile, convert(Color, color), thickness)

border(style::Any; color=colorant"black", thickness::Length=1pt) =
    tile -> Bordered(convert(BorderStyle, style), [left,right,top,bottom], tile, convert(Color, color), thickness)

The user can call it in two different ways:

border(dotted, [left], tile, color=colorant"blue") # => Bordered(Dotted(), [Left()], FooTile(), RGB(...))
tile |> border(dotted, [left], color=colorant"red") # => Bordered(Dotted(), [Left()], FooTile(), RGB(...))
border(dotted, tile, color=colorant"red")  # => Bordered(Dotted(), [Left(),Right(),Top(),Bottom()], FooTile(), RGB(...))
tile |> border(dotted, color=colorant"red") # => Bordered(Dotted(), [Left(),Right(),Top(),Bottom()], FooTile(), RGB(...))

Type parameters can be used in @api definitions, for example:

@api border => (Bordered{T <: Side} <: Tile) begin
end The render method

The connection between the Escher Tile, and the browser is done using the render method. A Tile is rendered into a Patchwork.jl Elem type and placed in the Virtual DOM.

The general format is as follow, but for detailed information please read the Patchwork.jl documentation:

render(e::TypeName, state) = Elem("custom-element", attributes = Dict(:htmlPropertyOne => e.fieldOne, :htmlPropertyTwo => e.fieldTwo))

The state object gets passed around when a Tile renders other tiles contained by it. It's just a plain dictionary, so the render methods can decide what to use it for.

4.3.4. Real life use

  • create custom Tiles with behavior, what are the ways to interact with HTML template's methods and events APIs
  • provide step-by-step example for creating assets

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