Hello everyone,
I found that a vector being associative really enlightening and
useful. But merge-with and other functions don't work, even though I
think it is not unreasonable to expect that. That is because
(seq [1 2 3 4]) is the seq of Long while (seq {0 1, 1 2, 2 3, 3
4}) is a seq of MapEntry, which merge-with relies on to work.
There are various ways to address this problem: map comes immediately to
mind. However I think there is an inconsistency in the definition of a
seq. Which could be addressed this way:
(defn associative-seq
([vector]
(associative-seq 0 vector))
([current-idx vector]
(reify
clojure.lang.ILookup
(valAt [this idx]
(nth vector idx))
(valAt [this idx not-found]
(nth vector idx not-found))
clojure.lang.Associative
(containsKey [this idx]
(< idx (count vector)))
(entryAt [this idx]
(clojure.lang.MapEntry. idx (nth vector idx)))
(assoc [this idx val]
(assoc vector idx val))
clojure.lang.ISeq
(first [this]
(if-let [fst (first vector)]
(clojure.lang.MapEntry. current-idx fst)
nil))
(next [this]
(if (seq vector)
(associative-seq (inc current-idx) (next vector))
(seq (first this))))
clojure.lang.Seqable
(seq [this]
(if-let [nxt (next this)]
(cons (first this) nxt)
nil)))))
Actually to make it consistent, the seq would only ever return the vals
of a map, while associative-seq would always contain MapEntries,
when the underlying datastructure can be interpreted as associative.
Thoughts?
Regards
Robert
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