Dynamically add user-created functions that satisfy an interface

Possible short answer:

Use a programming language that supports dynamic typing and higher-order functions, and define an interface that specifies the required functionality for the user-created functions. Then, at runtime, read the user's code and check if each user-defined function matches the interface, using methods such as duck typing, structural typing, or explicit type checking. Finally, store or execute the validated functions as needed, in a way that preserves the desired behavior and abstraction of the interface.

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