2557e3295f
Round 5 of the seed shrink. transduce is the canonical 5-liner over reduce
(which already honors reduced and steps lazy seqs); eduction composes with
comp and stays eager into a vector (documented divergence, as before);
td-comp — eduction's last caller — is deleted from the seed. transient
accepts tuples now (reader vectors / map entries), so (into [] (first {:a 1}))
keeps working everywhere a vector does.
into was moved, benched, and moved back: the overlay call layers cost the
into-vec suite ~11% back-to-back (536 vs 480ms), the same per-call wall that
sent even?/odd? home in round 4. A transient conj! fast path didn't pay for
itself either (jolt call overhead dominates, not the per-element conj). The
seed keeps core-into + its private transduce machinery; the binding count
still drops by three.
77 lines
4.5 KiB
Text
77 lines
4.5 KiB
Text
# Specification: transducers.
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(use ../support/harness)
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(defspec "transducers / into"
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["map xform" "[2 3 4]" "(into [] (map inc) [1 2 3])"]
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["filter xform" "[2 4]" "(into [] (filter even?) [1 2 3 4])"]
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["remove xform" "[1 3]" "(into [] (remove even?) [1 2 3 4])"]
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["take xform" "[1 2]" "(into [] (take 2) [1 2 3 4])"]
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["drop xform" "[3 4]" "(into [] (drop 2) [1 2 3 4])"]
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["take-while xform" "[1 2]" "(into [] (take-while (fn [x] (< x 3))) [1 2 3 1])"]
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["keep xform" "[1 3]" "(into [] (keep (fn [x] (if (odd? x) x nil))) [1 2 3 4])"]
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["map-indexed xform" "[[0 :a] [1 :b]]" "(into [] (map-indexed vector) [:a :b])"]
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["mapcat xform" "[1 1 2 2]" "(into [] (mapcat (fn [x] [x x])) [1 2])"]
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["cat xform" "[1 2 3 4]" "(into [] cat [[1 2] [3 4]])"]
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["into a set" "#{2 3 4}" "(into #{} (map inc) [1 2 3])"])
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# transducer comp applies left-to-right: (comp (map a) (filter b)) maps then filters
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(defspec "transducers / compose"
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["comp map+filter" "[2 4 6 8]" "(into [] (comp (map (fn [x] (* x 2))) (filter even?)) [1 2 3 4])"]
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["comp filter+map" "[2 4]" "(into [] (comp (filter odd?) (map inc)) [1 2 3 4])"]
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["comp three" "[2]" "(into [] (comp (map inc) (filter even?) (take 1)) [1 2 3 4])"])
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(defspec "transducers / transduce & sequence"
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["transduce sum" "9" "(transduce (map inc) + [1 2 3])"]
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["transduce init" "19" "(transduce (map inc) + 10 [1 2 3])"]
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["transduce filter" "6" "(transduce (filter even?) + [1 2 3 4])"]
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["sequence xform" "[2 3 4]" "(sequence (map inc) [1 2 3])"]
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["eduction" "[2 3 4]" "(into [] (eduction (map inc) [1 2 3]))"]
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["completing" "9" "(transduce (map inc) (completing +) 0 [1 2 3])"])
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# halt-when replaces the WHOLE reduction result with the halting input (or
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# with (retf acc input)) — Clojure's ::halt map protocol, unwrapped by the
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# transducer's completion arity.
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(defspec "transducers / halt-when"
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["halt returns the halting input" "7"
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"(transduce (halt-when (fn [x] (> x 5))) conj [1 2 7 3])"]
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["no halt is a plain reduction" "[1 2 3]"
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"(transduce (halt-when (fn [x] (> x 5))) conj [1 2 3])"]
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["retf combines acc and input" "[[1 2] 7]"
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"(transduce (halt-when (fn [x] (> x 5)) (fn [r i] [r i])) conj [1 2 7 3])"]
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["halt-when through into" "3"
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"(into [] (halt-when odd?) [2 4 3 6])"])
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# A `take`/`take-while` transducer returns `reduced`, which must short-circuit
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# the reduction so transducing over an INFINITE seq terminates rather than
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# realizing it eagerly.
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(defspec "transducers / short-circuit over infinite seqs"
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["into take (range)" "[0 1 2 3 4]" "(into [] (take 5) (range))"]
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["transduce take (range)" "3" "(transduce (take 3) + 0 (range))"]
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["sequence take (range)" "[0 1 2 3 4]" "(sequence (take 5) (range))"]
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["take-while over (range)" "[0 1 2]" "(into [] (take-while (fn [x] (< x 3))) (range))"]
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["comp take over (range)" "[1 3 5]" "(into [] (comp (filter odd?) (take 3)) (range))"]
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["into take iterate" "[0 1 2 3 4]" "(into [] (take 5) (iterate inc 0))"])
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# `reduce` itself honors `reduced`, so a reducing fn that returns `reduced`
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# terminates even over an infinite seq.
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(defspec "reduce / honors reduced"
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["reduced short-circuits inf" "105"
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"(reduce (fn [a x] (if (> a 100) (reduced a) (+ a x))) 0 (range))"]
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["reduce take inf" "10" "(reduce + (take 5 (range)))"]
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["reduce no-init first elem" "6" "(reduce + [1 2 3])"]
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["reduce no-init single" "42" "(reduce + [42])"]
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["reduce empty calls f" "0" "(reduce + [])"]
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["reduce with-init" "16" "(reduce + 10 [1 2 3])"]
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["reduce reduced immediate" ":x" "(reduce (fn [a x] (reduced :x)) :init [1 2 3])"])
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# into/transduce/eduction are overlay fns now (seed-shrink round 5): into
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# takes a transient fast path for vectors and preserves metadata; eduction
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# stays eager (documented divergence).
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(defspec "transducers / into & eduction (overlay)"
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["into list prepends" "(quote (4 3 1 2))" "(into (quote (1 2)) [3 4])"]
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["into sorted-map" "{1 :a, 2 :b}" "(into (sorted-map) [[2 :b] [1 :a]])"]
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["into from map entry" "[:a 1]" "(into [] (first {:a 1}))"]
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["into xform on map" "{:a 2}" "(into {} (map (fn [e] [(key e) (inc (val e))])) {:a 1})"]
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["eduction multiple xforms" "[4]" "(into [] (eduction (filter odd?) (map inc) [2 3 4]))"]
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["->Eduction" "[2 3]" "(->Eduction (map inc) [1 2])"]
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["transduce no init uses (f)" "5" "(transduce (map inc) + [1 2])"])
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