Splitting a Schema — ASL

Splitting a Schema

A schema does not have to live in one file. Point schema-path at a glob, and Axel reads every matching .asl file and merges them into one schema:

axel.yaml

schema-path: schema/*.asl

schema/
  base.asl      # abstract types shared by everything
  user.asl
  post.asl
  functions.asl

Every command that takes a schema accepts the same forms:

Form	Meaning
schema.asl	a single file
schema/	a directory, walked recursively for .asl files
schema/*.asl	every .asl directly inside schema/
schema/**/*.asl	every .asl under schema/, at any depth

axel validate --schema 'schema/*.asl'
axel codegen --schema-path 'schema/**/*.asl' -g go -o ./gen

Quote the pattern so Axel expands it rather than your shell — that way ** works the same everywhere.

If you run axel -d ./myproject with no axel.yaml, a schema/ directory in the project is picked up automatically once schema.asl and default.asl are absent.

One flat namespace

There is no import and no per-file scoping. The files are concatenated, so a declaration in one file is visible from all the others:

schema/base.asl

abstract type Base {
  required id: uuid { default := gen_uuid(); constraint pk; };
}

schema/post.asl

type Post extends Base {
  required title: str;
  required link author: User;   # User lives in schema/user.asl
}

Order never matters — not within a file, and not between files. A type may extend a parent declared in a file that is read later, and a link may point at a type declared anywhere in the set.

use extension is deduplicated, so each file is free to declare the extensions it depends on:

use extension 'uuid-ossp';

Duplicate names are an error

Because the files share one namespace, declaring the same name twice is rejected, and the error names both locations:

resolving schema: type "User" declared more than once (schema/user.asl:3:1 and schema/billing.asl:14:1)

The same applies to enums, scalar aliases, globals and functions — and across kinds, so an enum and a type cannot share a name either.