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MEL ​

Purpose: Overview of MEL (Manifesto Expression Language) Audience: Anyone writing or reviewing Manifesto domains Reading time: 5 minutes

What is MEL? ​

MEL (Manifesto Expression Language) is a declarative, typed language for defining Manifesto domains. It compiles to DomainSchema, which Core evaluates deterministically.

MEL is designed for:

  • Human authored domain definitions
  • LLM authored domain definitions
  • Build-time validation and review

Where MEL fits ​

MEL source -> @manifesto-ai/compiler -> DomainSchema -> Core -> Host

MEL is a source format. It does not execute. It produces data that Core can compute on.

What MEL is NOT ​

  • Not a general-purpose language
  • Not a workflow engine
  • Not an effect executor
  • Not a runtime

Quick Example ​

mel
domain Counter {
  state {
    count: number = 0
    lastIntent: string | null = null
  }

  computed doubled = mul(count, 2)

  action increment() {
    once(lastIntent) {
      patch lastIntent = $meta.intentId
      patch count = add(count, 1)
    }
  }
}

MEL vs Builder ​

If you want...Use
TypeScript-first authoring@manifesto-ai/builder
A source language for humans and LLMsMEL + compiler
Build-time validation and reviewMEL + compiler

Both paths produce the same DomainSchema for Core.

CLI: check and compile ​

bash
pnpm add -D @manifesto-ai/compiler
pnpm exec mel check path/to/domain.mel
pnpm exec mel compile path/to/domain.mel --stdout