"Many languages (not necessarily scripting languages) support extending through an FFI (foreign function interface). An FFI is not enough to allow a function in the system language to do all that a function in the script can do. Nevertheless, in practice FFI covers most common needs for extending, such as access to external libraries and system calls. Embedding, on the other hand, is harder to support, because it usually demands closer integration between the host program and the script, and an FFI alone does not suffice.""
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