replant

Kotlin to TypeScript data-structure transpiler

Uses tree-sitter via Node.js bindings with Kotlin grammar

Status

Prototype - proof of concept

Goals

• The focus lies on transpiling data classes or POJOs. It is not planned to try to convert any logic.
• Simplicity (usage of the tree-sitter AST is even easier than using regular expressions?)
• Resistant to syntax changes (compared to regular expressions)
• Easy to adapt to different source (and output?) languages

Examples

Data classes

Kotlin input:

data class Apple(
    var id: Long?,
    val color: String,
    val size: Int,
    val updated: LocalDate
)

Generated TypeScript output:
(At least that is what is planned, we are not there yet)

interface IApple {
    readonly id: number | null
    readonly color: string
    readonly size: number
    readonly updated: Date
}
export class Apple implements IApple {
  constructor (
    public readonly id: number | null,
    public readonly color: string,
    public readonly size: number,
    public readonly updated: Date,
  ) {}
  copy(update: Partial<Apple>): Apple {
    return /* new object with updated fields */
  }
  static from(obj: IApple): Apple {}
}

Enums

… tbd …

Development

This project currently uses shadow-cljs to compile ClojureScript. This makes it very easy to add npm dependencies and requires nearly zero configuration.

1. (Optionally) shadow-cljs server start Speeds up the following commands
2. shadow-cljs watch :test to compile the :test target (and recompile on changes)

Comparison to alternative implementations

Regular Expressions

Pros:

• Simple

Cons:

• Prone to unforseen syntax changes

Annotation Processor

Pros:

• Integrated into compilation via kapt, no extra setup (but not with IntelliJ’s build system)

Cons:

• Integrated into compilaton, can’t be run on it’s own
• kapt the Kotlin annotation processing tool is quite slow
• The Java annotation processing API is not easy to use with Kotlin sources