Result demo application

Some time ago I wrote a blog post with some tips, tricks, and techniques for effective use of the Result type (and Validation type)! I highly recommend going through this previous post if you have not read it yet!

Here's a quick recap:

Tips

• Use a Discriminated Unions for the error type in a Result
• If you care about all the errors rather than just the first encountered error, use a validation

Tricks

• How to combine different types of errors, useful for pipelines or validation which may be the combination of different types of error.
• How to filter out only the errors we care about from a list of errors

I thought it might be useful to create a SAFE application to demonstrate how someone might chain some of these techniques together.

https://github.com/CompositionalIT/username-signup-result-demo

Notable features:

Thanks to Fable we only need to write the validation in one place - then it can be run in the broswer and also server-side.

• Local validation

  • Quick
  • Insecure, can be bypassed by users
  • Can't do all checks e.g. DB checks

• Remote validation

  • Slower (requires a network round trip)
  • Secure - can't be skipped!
  • More accurate e.g. Can perform DB checks