*Description*
Updatable folds are a notion connected to FunctionalTransformationSystems.
*Explanation*
The bottom-up traversal scheme associated to a multi-sorted signature, or a system of mutually dependent datatypes, is captured by a family of _fold functions_. These fold functions are parameterized with a _fold algebra_, which stores the functions to be applied at each node during traversal. A fold algebra can be constructed by applying _fold algebra updates_ to a _basic fold algebra_.
These notions were coined in DealingWithLargeBananas, and they were used in the FunctionalTransformationSystemsPaper and in StrategiesAsUpdatableFoldAlgebras.
*Examples*
For a concise example of updatable folds and their application to program transformation, see the FunctionalTransformationSystemsPaper.
*See also*
FunctionalTransformationSystems