transduceable

[ transduce\wrap:, transduce\step: ]

The transduceable protocol defines how a value serves as a transducer.

Reduce means to lead back. Think of a reducer as a function which leads a sequence of values back towards a single value.

Transduce is an invented word (by Rich Hickey afaik), and the root trans means across, changing the meaning of the word to to bring across. Think of a transducer as leading a sequence of values across or through some transformation.

Therefore, a transducer’s job is to wrap a reducer, and manipulate the values passed through to the reducer, without it ever having to know.

The fundamental utility of a transducer is that it defines when a reducing function is called.

For example, the filter: transducer ensures that the reducing function is only called when values meet a certain condition.

To accomplish this, a transduceable must implement two messages, wrap and step.

transduce\wrap: wraps the argument reducing function with the self transducer.

This gives the transducer somewhere to send the values it brings across.

In order to transduce values, the transducer should implement transduce\step:.

This is conceptually similar to reduce\step: for the reduceable: protocol, but has a different signature.

In addition to receiving an accumulator and tuple of values from the sequence, transduce\step: receives a reduceable and a state argument as well.

transduce\wrap

transduceable.transduce\wrap: reducer reduceable: => reduceable:

Wrap a reduceable with some behavior, returning a new reduceable.

transduce\step

transduceable.transduce\step: (reducer reduceable:, accumulator unknown, sequence List[unknown], state unknown) => (state unknown, command next: | stop:, reducer reduceable:, accumulator unknown)

Step the transducer. This may call the wrapped reduceable any number of times per step.