>From the docs:
r/fold takes a reducible collection and partitions it into groups of
approximately n (default 512) elements. Each group is reduced using the
reducef function. The reducef function will be called with no arguments to
produce an identity value in each partition. The results of those
reductions are then reduced with the combinef (defaults to reducef)
function. When called with no arguments, (combinef) must produce its
identity element - this will be called multiple times. Operations may be
performed in parallel. Results will preserve order.
So, this seems to say r/fold will partition the collection and reduce each
partition using the (reducef) as the init value.
Then, all these intermediate results will be reduced with combinef, using
(combinef) as the init value.
However, in test it seems (reducef) is never called, and (combinef) is used
as the init value for calls to reducef.
(defn combinef
([] {:combine :f})
([acc v] acc))
(defn reducef
([] {:reduce :f})
([acc v]
(println "acc" acc "v" v)
v))
(clojure.core.reducers/fold combinef reducef ["foo" "bar"])
; outputs:
acc {:combine :f} v foo
acc foo v bar
"bar"
The accumulator in reducef is the init value from combinef, not the init
value from reducef.
What's going on?
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