: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

: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.

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");
```

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