How deeply does Clojure: The Essential Reference cover stateful transducer?

Shows internal initialization, buffering, reducing, and teardown, but does not develop a general implementation beyond the partition-all example.

Stateful transducer

As explained in Clojure: The Essential Reference

A stateful transducer is a transducer that retains partial processing state until it receives a signal that reduction is complete.

A stateful transducer retains partial processing state until reduction finishes. This matters when a transformation buffers or accumulates data, because receiving the final item does not necessarily flush that state. transduce signals completion by calling the reducing function with one argument, allowing the transducer chain to release buffered results consistently. section 7.2.3

Completion flushes partition-all

With (partition-all 3), two inputs remain buffered until the final reducing-function call: (xform-reductor 0 0) ; 0 (xform-reductor 0 0) ; 0 (xform-reductor 0) ; #done! 2 Without that final one-argument call, the buffered values would not be emitted and the result would remain 0. section 7.2.3

(def xform                              ; #1
  (comp (map inc)
        (partition-all 3)
        cat))

(def xform-reductor                     ; #2
  (xform
    (completing +
      #(do (print "#done! ") %))))

(xform-reductor 0 0)                    ; #3
;; 0
(xform-reductor 0 0)                    ; #4
;; 0
(xform-reductor 0)                      ; #5
;; #done! 2

Inspect the reducing function and its final one-argument completion call. section 7.2.3

How Clojure: The Essential Reference covers it

Cover of Clojure: The Essential Reference

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Related concepts

transducerkind of · A transducer is a composable transformation that processes inputs independently of the context in which the transformation is consumed.
completingaddressed by · completing is a Clojure function that adapts a binary reducing function with completion behavior for use as a transducer reducing function.
partition-allincludes · partition-all is a Clojure function that divides a collection into subsequences of up to a requested size, retaining a final smaller subsequence when necessary.

This explainer was generated by Manning's knowledge graph from the text of Clojure: The Essential Reference. The section links point to the parts of the book it draws on.