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External

external，或叫 “FFI”（foreign function interface），或者更简单叫做 “interop” （interoperability 的缩写），帮助 Reason 与其他语言交流，像 C 和 JavaScript。

想象一个 let 绑定，省略实体，但是标注了类型（强制）声明。

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.