CLAUDE.md for Scala: 13 Rules That Make AI Write Idiomatic Functional Code

The rules outlined in the document are best practices for writing robust, maintainable, and error-handling-friendly Scala code using functional programming principles. Here's a summary of each rule:

Rule 1: Domain Models as Case Classes with Validation

Why:

• Ensures data integrity by validating input before it reaches business logic.
• Makes the codebase more readable and easier to reason about.

Bad Example:

scala
 
1case class User(name: String, email: String)

Good Example:

scala
 
1import zio.{ZIO, Task}
2import zio.prelude.Validation
3
4case class SignupRequest(email: String)
5
6object Validation {
7  def validate(req: SignupRequest): ZIO[Any, ValidationError, Unit] = 
8    for {
9      _ <- checkEmailFormat(req.email)
10      // other validations...
11    } yield ()
12}
13
14sealed trait ValidationError
15final case class InvalidEmailFormat(message: String) extends ValidationError
16
17def checkEmailFormat(email: String): Task[ValidationError] =
18  if (email.matches("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}")) ZIO.succeed(())
19  else ZIO
20
21[Read the full article at DEV Community](https://dev.to/olivia_craft/claudemd-for-scala-13-rules-that-make-ai-write-idiomatic-functional-code-3cgi)
22
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