In functional programming, 'fold' is a higher-order function that processes a data structure, such as a list, to produce a single cumulative result. It operates by recursively applying a binary function to elements of the structure and an accumulator, allowing for operations like summation, product, or transforming data while managing state throughout the process. This concept is crucial in error handling and state management as it enables encapsulating side effects and maintaining context in computations.
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