Op.ValueA second input value, which is not part of the key (so there can be only one value for any key at one time). For outputs, this is used to hold the value to which the output should be set. For builds, non-essential inputs can be placed here instead of in the key so that the old outcome can be latched for minor changes. For example, when testing a Git commit the commit to test would be the key, but the latest version of the test platform might be the value.
val digest : t -> stringdigest t is a unique string for t that can be used as a primary key in a database. Two ts are considered equal if they have the same digest.