Consume ensures that the specified method is called on the value when it is computed, and before other computables that depend on the return value of Consume.

Continuously computes `sinkable` and recomputes it on any tansitive change to `sinkable`'s inputs.

Configurable globally only for now.

ErrDoneSinking is used as a return value from Updated to indicate that no more action will be taken and Sink() should return.

If enabled, does not use cached contents, but still verifies that if we do have cached contents, they match what we produced.

A Computable whose lifecycle is bound to the surrounding Do() invocation.

A Computable whose lifecycle is bound to the environment where it is computed.

This Computable embeds a "precomputed" value and Compute() is guaranteed to return immediately.

A computable represents a node in a computation graph.