To continue on my previous post, here is the implementation of map
which returns both reducible and (lazy)seqable collection:
(defn my-map
[f c]
(let [coll (clojure.core.reducers/map f c)
d (delay (clojure.core/map f c))]
(reify
clojure.core.protocols/CollReduce
To continue on my previous email, here is the implementation of map which
returns both reducible and (lazy) seqable object:
(defn my-map
[f c]
(let [coll (clojure.core.reducers/map f c)
d (delay (clojure.core/map f c))]
(reify
clojure.core.protocols/CollReduce
To continue my previous email, here is the implementation of map which is
both reducible and (lazy) seqable:
(defn my-map
[f c]
(let [coll (clojure.core.reducers/map f c)
d (delay (clojure.core/map f c))]
(reify
clojure.core.protocols/CollReduce
(coll-redu
Gaving slept on it I realize that by adding before popping I allowed the
buffer to grow to n+1 thus causing a realloc.
(defn drop-last [n coll]
(reducer coll
(fn [f1]
(let [buffer (java.util.ArrayDeque. (int n))]
(fn self
([] (f1))
([ret x]
(let
Wow, thank you very much! A perfect solution.
At the end, wouldn't be good if the reducers would implement alongside
CollReduce also a Seqable interface, so that reducers could be used as a
drop in replacement for today's sequence functions (map, filter, ...)?
CollReduce implements 'eager' comp
ArrayDeque based versions:
(defn drop-last [n coll]
(reducer coll
(fn [f1]
(let [buffer (java.util.ArrayDeque. (int n))]
(fn self
([] (f1))
([ret x]
(.add buffer x)
(if (<= (count buffer) n)
ret
(f1 ret (.p
You need to use a buffer to defer calls to the reduced function
(defn drop-last [n coll]
(reducer coll
(fn [f1]
(let [buffer
(atom clojure.lang.PersistentQueue/EMPTY)]
(fn self
([] (f1))
([ret x]
(let [b (swap! buffer conj x)]
Is it possible to implement efficient butlast (and drop-last, take-last)
with reducers? The only solution I can think of needs additional reduce to
compute count, which may often be undesirable.
Or is it OK to say that reducers are not designed for such cases?
JW
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