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External

external，或 "FFI"（外來函式界面），或簡單地 "交互"（ 意思是 "交互作用性"）是 Reason 如何與其他語言進行溝通，像是 C 或 JavaScript。

Imagine writing a let binding, but with its body omitted and its (mandatory) type written down:

external myCFunction: int => string = "theCFunction";

Note: externals can only be at the top level, or inside a module definition. You can't declare them in e.g. a function body.

用法

You'd use an external value/function as if it was a normal let binding.

For more infos on how to link up your C functions within your Reason application, have a look at the Dealing with foreign libraries section in the dune build system docs.