scala and state monad: no free lunch part 2

As a follow up to my last post about no free lunch I wanted to show more state monad usage and recognize that you can change function return types in the middle of a for-comprehension. This allows each function to return different types of values from the computation along the way.

In the code below, you compose a function by using the for-comprehension. The yield part of the for-comprehension is a State object. When that state object is called, it returns a tuple of (state, value). You can use ._1 or ._2 to obtain the value of interest.

The last composed function shows an example of changing the state type (instead of changing the returned value type mentioned above)  in the middle of the for-comprehension using scalaz IndexedState's iPut and iModify. This allows you to change the type of state as you go to adapt to different function's API needs.

The entire article is at gisthub.

Comments

Post a Comment

Popular posts from this blog

quick note on scala.js, react hooks, monix, auth

quick note on scala.js, react hooks, monix, auth Reactjs hooks finally came out of preview in a recent version of React. scalajs-reaction has had support for hooks since they were in preview. React hooks seem like the hot new thing but for me the question is, do hooks help improve your code by improving maintainability, time to market, TCO, etc.? Let’s take a look using authentication as an example and employ monix , a reactive observable framework that also builds on cats . We will assume we are building a SPA. Does it improve your code and make your application & development experience better? Auth Auth processing can be complex. Many react auth examples you find in blogs like to show how to use “react-routing” and “auth” as a switch that determines which routes are protected or unprotected. Protected routes show application specific data. Unprotected routes show login content . Based on storing a “User” object in the browser session/local storage, th...
Read more

zio environment and modules pattern: zio, scala.js, react, query management

zio environment and modules pattern: zio, scala.js, react, query management This blog covers a zio-based fetch design for scala.js, react web applications. It heavily uses the zio “environment” feature to help motivate a point of view on the modules pattern in effect systems. At the end, I summarize some thoughts on ergonomics and complexity. This blog assumes a basic knowledge of zio and react. scala.js is just like scala so you mostly already know scala.js. This blog is a follow-on to previous blogs: https://appddeevvmeanderings.blogspot.com/2019/10/scalajs-react-fetcher-hook_48.html and https://appddeevvmeanderings.blogspot.com/2019/11/scalajs-and-react-suspense.html . I have been keeping an eye on and culling ideas from typscript/javascript fetching libraries that address query management concerns. The formulation below incorporates some of those concerns but does not try to comprehensively duplicate well established javascript libraries. I only care about ...
Read more

attributes with react and typescript.md

If you use typescript with react you may wonder what the right signature is for your “properties” interface. Obviously, your component will have few to many specific properties that reflect your domain. However, you may wish to also provide for the ability to add other attributes, such as those valid for a div property. In other words, you want to extend your props interface with that of the properties from a div element. How do you do that? There are really two issues: How do you extend your props interfaces How do you filter the props once you receive them to just those that apply. Extend Your Prop Interface or Use Sum Types It’s not uncommon to see interface Props { className ? : string yourProp ? : number } with the idea of using it in class MyComponent extends React.Component<Props, any> somewhere. If your component will have an outer div, you may also pass in a react element so that its configurable. But let’s say your outer element is a div and you wan...
Read more