:sig
DTree* unit_call(String file_name, String function_name, DTree* call_param = null)

:params
file_name : UCE file to load and execute
function_name : name of the function to invoke
call_param : optional, call parameter
return value : DTree* returned from function

:see
>ob
unit_load
unit_render
unit_info
1_RENDER
1_COMPONENT

:content
Calls an exported function inside another UCE file.

Use `unit_call()` when you need structured data exchange between units rather than rendered HTML output.

The callee must expose an `EXPORT` function whose name matches `function_name`. Arguments are passed through `call_param`, and the return value is a `DTree*` owned by the callee.

`unit_call()` also understands the request-bound UCE entrypoint names:

- `RENDER`
- `RENDER:NAME`
- `COMPONENT`
- `COMPONENT:NAME`
- `ONCE`
- `INIT`

When `function_name` matches one of those macro-style entrypoints, `unit_call()` does not look for a plain `EXPORT DTree* ...` function. Instead, it translates the name to the generated C++ symbol, uses the current `Request` context, and passes `call_param` into `context.props`, matching the normal component invocation model.

For `RENDER...` and `COMPONENT...`, the unit's `ONCE(Request& context)` hook is still honored automatically before the selected handler runs.

Example:

```cpp
// export a function
EXPORT DTree* test_func(DTree* call_param)
{
	print("HELLO FROM TEST FUNCTION");
	return(0);
}

// use that function in another file
unit_call("call_file_funcs.uce", "test_func");
```

Calling a named component handler through `unit_call()`:

```cpp
DTree props;
props["title"] = "Diagnostics";
props["body"] = "Ready";

unit_call("components/card.uce", "COMPONENT:BODY", &props);
```

Calling a page render handler through `unit_call()`:

```cpp
DTree props;
props["section"] = "summary";

unit_call("reports/summary.uce", "RENDER", &props);
```

Related:

- PHP: `include`, `require`, or calling a function from an included module, especially when returning arrays or objects instead of rendering a view
- JavaScript / Node.js: importing a module and calling an exported function, or dynamically loading a module and passing structured arguments