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https://github.com/Niminem/Neel

A Nim library for making Electron-like HTML/JS GUI apps, with full access to Nim capabilities.
https://github.com/Niminem/Neel

desktop-app desktop-application electron electron-app gui gui-application nim nim-gui nim-lang nim-language nim-library

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A Nim library for making Electron-like HTML/JS GUI apps, with full access to Nim capabilities.

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README 

        
# Neel | HTML/JS GUI Library for Nim



Neel is a Nim library for making lightweight Electron-like HTML/JS GUI apps, with full access to Nim capabilities and targets any of the C, C++, or Objective-C backends.



> By default, Neel opens a new Chrome session in app mode and allows the Nim backend and HTML/JS frontend to communicate via JSON and websockets. Alternate mode available, simply opening a new tab in your system's default browser. Webview capabilities coming soon.



Neel is designed to take all the hassle out of writing GUI applications. Current Features:



* Eliminate 99% of boilerplate code

* Automatic routes

* Embeds frontend assets at compiletime (on `release` builds)

* Automatic type conversions (from JSON to each procedure's parameter types)

* Simple interface for backend/frontend communication

* Cross-platform (tested on Mac, Windows, and Linux)



Neel is inspired by [Eel](https://github.com/samuelhwilliams/Eel), its Python cousin.



----------------------



## Introduction



Currently, Nim’s options for writing GUI applications are quite limited and if you wanted to use HTML/JS instead you can expect a lot of boilerplate code and headaches.



Neel is still in its infancy, so as of right now I don’t think it’s suitable for making full-blown commercial applications like Slack or Twitch. It is, however, very suitable for making all kinds of other projects and tools.



The best visualization libraries that exist are in Javascript and the most powerful capabilities of software can be harnessed with Nim. The goal of Neel is to combine the two languages and assist you in creating some killer applications.



## Installation



Install from nimble:

`nimble install neel`



## Usage



### Directory Structure



Currently, Neel applications consist of various static web assets (HTML,CSS,JS, etc.) and Nim modules.



All of the frontend files need to be placed within a single folder (they can be further divided into more folders within it if necessary). The starting URL must be named `index.html` and placed within the root of the web folder.



```

main.nim            <----\

database.nim        <-------- Nim files

other.nim           <----/

/assets/             <------- Web folder containing frontend files (can be named whatever you want)

  index.html        <-------- The starting URL for the application (**must** be named 'index.html' and located within the root of the web folder)

  /css/

    style.css

  /js/

    main.js

```



### Developing the Application



#### Nim / Backend



We begin with a very simple example, from there I'll explain the process and each part in detail.



(main.nim)

```nim

import neel #1



exposeProcs: #2

    proc echoThis(jsMsg: string) =

        echo "got this from frontend: " & jsMsg

        callJs("logThis", "Hello from Nim!") #3



startApp(webDirPath="path-to-web-assets-folder") #4

```



##### #1 import neel



When you `import neel`, several modules are exported into the calling module. `exposedProcs` and `startApp` are macros that require these modules in order to work properly. The list below are all of the exported modules. It's not necessary to remember them, and even if you accidently imported the module twice Nim disregards it. This is just for your reference really.

* `std/os`

* `std/osproc`

* `std/strutils`

* `std/json`

* `std/threadpool`

* `std/browsers`

* `std/jsonutils`

* `pkg/mummy`

* `pkg/routers`



##### #2 exposeProcs



`exposeProcs` is a macro that *exposes* specific procedures for javascript to be able to call from the frontend. When the macro is expanded, it creates a procedure `callNim` which contains **all exposed procedures** and will call a specified procedure based on frontend data, passing in the appropriate parameters (should there be any).



The data being received is initially **JSON** and needs to be converted into the appropriate types for each parameter in a procedure. This is also handled by the macro.



As of Neel 1.1.0, you can use virtually any Nim type for parameters in *exposed procedures*. Neel uses `std/jsonutils` to programmatically handle the conversions. Some caveats:

* Does not support default values for parameters.

* Does not support generics for parameters.



This above macro produces this result:



```nim

proc callNim(procName: string; params: seq[JsonNode]) =

    proc echoThis(jsMsg: string) =

        echo "got this from frontend: " & jsMsg

        callJs("logThis", "Hello from Nim!")

    case procName

    of "echoThis": echoThis(params[0].getStr)

    ...

```



NOTE: You *can* pass complex data in a single parameter now if you'd like to. Use Javascript objects or dictionaries and simply create a custom object type to accept it from the Nim side.



I'm sure this is obvious, but it's much cleaner to have your exposed procedures call procedures from other modules.



Example:

```nim

# (main.nim)

import neel, othermodule

exposeProcs:

    proc proc1(param: seq[JsonNode]) =

        doStuff(param[0].getInt)

...



# (othermodule.nim)

from neel import callJs # you only need to import this macro from Neel :)



proc doStuff*(param: int) =

    var dataForFrontEnd = param + 100

    callJs("myJavascriptFunc", dataForFrontEnd)

...

```



##### #3 callJs



`callJs` is a macro that takes in at least one value, a `string`, and it's *the name of the javascript function you want to call*. Any other value will be passed into that javascript function call on the frontend. You may pass in any amount to satisfy your function parameters needs like so:



```nim

callJs("myJavascriptFunc",1,3.14,["some stuff",1,9000])

```



The above code gets converted into stringified JSON and sent to the frontend via websocket.



##### #4 startApp



`startApp` is a macro that handles server logic, routing, and Chrome web browser. `startApp` currently takes 6 parameters.

example:



```nim

startApp(webDirPath= "path_to_web_assets_folder", portNo=5000,

            position= [500,150], size= [600,600], chromeFlags= @["--force-dark-mode"], appMode= true)

            # left, top          # width, height

```



* `webDirPath` : sets the path to the web directory containing all frontend assets **needs to be set**

* `portNo` : specifies the port for serving your application (default is 5000)

* `position` : positions the *top* and *left* side of your application window (default is 500 x 150)

* `size` : sets the size of your application window by *width* and *height*(default is 600 x 600)

* `chromeFlags` : passes any additional flags to chrome (default is none)

* `appMode` : if "true" (default) Chrome will open a new session/window in App mode, if "false" a new tab will be opened in your *current default browser* - which can be very useful for debugging.



#### Javascript / Frontend



The Javascript aspect of a Neel app isn't nearly as complex. Let's build the frontend for the example above:



(index.html)

```html



    

    

    Neel App Example

     



    
My First Neel App


     



```

(main.js)

```javascript

neel.callNim("echoThis","Hello from Javascript!")



function logThis(param){

    console.log(param)

}

```

The first thing you'll notice is we've included a script tag containing `/neel.js` in the  section of our HTML page. This allows Neel to handle all of the logic on the frontend for websocket connections and function/procedure calls.



`neel.callNim` is a function that takes in at least one value, a `string`, and it's *the name of the Nim procedure you want to call*. Any other value will be passed into that Nim procedure call on the backend asa parameter. **You must pass in the correct number of params for that proc, in order, and of the correct types for it to be called properly.** Example: 



frontend call to backend:

```javascript

neel.callNim("myNimProc",1,3.14,["some stuff",1,9000])

```

must match the result of the `exposeProcs` macro:

```nim

...

of "myNimProc": return myNimProc(params[0].getInt,params[1].getFloat,params[2].getElems)

...

```



As of Neel 1.1.0, there is exception handling in place (with a verbose logging in debug builds) for unknown procedure calls and parameter type mismatches.



Going back to our first example, when `index.html` is served, Javascript will call the `echoThis` procedure and pass "Hello from Javascript!" as the param. This will print the string in the terminal. Then, Nim will call the `logThis` function and pass "Hello from Nim!". Neel handles the JSON conversion, calls the function and passes in the param.



Now open the console in Chrome developer tools and you should see "Hello from Nim!".



**Keep In Mind: absolute paths must be used within your HTML files** ex: `