Custom function kinds, types, and decorators

Use custom only when the universal schema has no field for the kind of declaration. Do not put if syntax in custom.

custom is a free object in the template. The engine reads these arrays if present:

"custom": {
  "function_kinds": [
    {
      "name": "command",
      "declaration_keywords": ["command"],
      "description": "Host-invoked command. Same call semantics as fn."
    },
    {
      "name": "quest",
      "declaration_keywords": ["quest"],
      "description": "A scripted quest hook."
    }
  ],
  "types": [
    {
      "name": "entity",
      "declaration_keywords": ["entity"],
      "description": "Named map of fields the host may interpret."
    },
    {
      "name": "item",
      "declaration_keywords": ["item"],
      "description": "Item definition block."
    }
  ],
  "decorators": [
    {
      "name": "export",
      "prefix": "@",
      "description": "Register with the host on load."
    },
    {
      "name": "tick",
      "prefix": "@",
      "description": "Run every frame from C++."
    }
  ],
  "host_functions": ["print", "spawn", "damage"]
}

Also add those keywords to keywords.reserved / declaration / control_flow as appropriate so they tokenize as keywords. The reader appends declaration_keywords from custom kinds onto the function-keyword list automatically.

Function kinds

command ping() { return "pong"; } parses like fn ping() { ... }. The keyword is whatever you listed. Host:

engine.call("ping");

Several kinds can coexist (fn, command, quest). They share the same runtime function object.

Types

entity Portal {
  x = 10;
  y = 4;
  dest = "keep";
}

After run, engine.get("Portal") is a map with string keys. The host decides that this map is a “portal.”

Fields are name = expression. Separators: comma or statement terminator.

Decorators

@tick
@export
command think() {
  return 0;
}

Multiple prefixes in a row are allowed. Each name is looked up in bind_decorator. Unknown decorator names are ignored (no error). If the user wanted a hard failure, check the name in a catch-all hook or validate after load by walking get.

What custom is not for

• Renaming if — use control_flow.conditional.if_keywords
• New operators — use operators / custom_operators in the template; engine uses operators.* and precedence
• Entirely different JSON shapes — forbidden
• Language-specific C++ in ReScripted — forbidden

Document every custom kind’s meaning in description so the next agent does not guess.