chespinoza / order-taking

Idris version of Domain Modeling Made Functional Book.

Idris Full Stack DDD NodeJS example

Order Taking Service

Idris version of Domain Modeling Made Functional Book.

The Domain Modeling Made Functional by Scott Wlaschin introduces domain driven design and shows how well it fits to the world of functional programming via the lens of the F# programming language. As Scott showed us that DDD is indeed a nice fit for functional programming, questions arise naturally; could we push further the abstractions if we use a dependently typed programming language, like Idris? Where are the sweet spots of depedent types in the world of everyday programming? Everyday programming needs to be focused on delivery, maintanability, reliability, and being correct. The sad truth is that many applications needs to be more maintanable than correct. Being correct is not a clear concept because its meaning changes as the software evolves. In many cases, stakeholders only get a deeper understanding of the domain as the software solution/product evolves over time. In this setting, depedent typed programming helps us achieve maintanability rather than being correct. In this repository I show a simple layered architecture and I show how to use simple dependent types to draw explicit connections between the high level design of a service and its NodeJS deployed implementation. Ideas and practices originated, but reshuffled from the Type Driven Development with Idris by Edwin Brady and the Domain Modeling Made Functional by Scott Wlaschin. This architecture includes; An abstraction to talk about Bounded Context and Workflow, type safe description of a state transition system, a free monad approach for domain implementation, and an actual implementation of the domain on NodeJS back-end. Because of dependent types, this architecture becomes explicit, rather than implicit, meaning that connections between the high level design and the low level implementation are done via functions, changing the code anywhere requires to think at the whole, as possible type errors propagates to top or to bottom. Idris could immensely benefit from simple FFIs for NodeJS libraries. The FFIs would grant access to thousands of libraries from the NodeJS ecosystem almost for free. This approach would position Idris to be used even in production settings and the Idris userbase could be bootstrapped, later the Idris version of these libraries could be written.

Request: Please consider buying both of the books mentioned above. Boths are excellent resources for further studying of the applied subject.

Notes

This project meant to be a blue-print, example for micro-services written in Idris. Its main focus is to reproduce abstractions in dependently typed setting, that can be found in Scott Wlashin's book. The main focus is around the dependently typed implementation of BoundedContext, but several other parts of the architecture had to be worked on to be able to demostrate that Idris can host such solutions. Although during the implementation many other problems were required to think about in the dependently typed setting. This repository can be considered as a mine practices for dependently typed software development. Enjoy digging up those gems.

You may find the style of the explanations strange, maybe a bit chaotic, but if you follow path suggested in the READMAP.md you will learn many things about the Idris language. This style feels chaotic that could be because I have a slight ADHD and I try to linarize the content here, but sometimes quickly the explanations go deep. Although I believe a short explanation after every Idris snippet helps to view this reposity as a hand-book for Idris development.

High level overview

See the slides

Support

Run

After setted up; start the microservice with make start-opt, start the client service npm run dev, and open localhost:5000 in a browser.

Setup

Server

Install Idris2, its version can be found in the VERSIONS file.

For dependencies install nodejs, npm and packages:

npm install google-closure-compiler
npm install sqlite
npm install md5

To start the OrderTaking service, which will create the initial Sqlite DB and starts the service on 127.0.0.1:3000

make start-opt

Client

An example client can be found in the client/svelte-client directory. Follow the instructions from its README.md

To run the client, call the following command:

cd client/svelte-client
npm run dev

Which starts the client in development mode, any changes in its code, will be picked up.

Have fun!

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