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What is the difference between the functions seq? sequential? and coll?
I found some information scattered throughout the internet, but I think it would be better to centralize that information here.
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"Collection" and "Sequence" are abstractions, not a property that can be determined from a given value. Collections are bags of values. Sequence is a data structure (subset of collection) that is expected to be accessed in a sequential (linear) manner.
Clojure defines many algorithms in terms of sequences (seqs). A seq is a logical list, and unlike most Lisps where the list is represented by a concrete, 2-slot structure, Clojure uses the ISeq interface to allow many data structures to provide access to their elements as sequences.
seq? is a predicate that returns true if it's argument implements ISeq interface, which is to say it provides the methods first,rest,cons. See http://clojure.org/sequences.
(seq? [1 2]) false (seq? (seq [1 2])) true sequential? is a predicate that returns true if it's argument implements Sequential interface. Sequential is a marker interface (no methods) and is a promise that the collection can be iterated over in a defined order (e.g. a list, but not a map).
(sequential? []) true (sequential? {}) false coll? is a predicate that returns true if its argument implments IPersistentCollection. So for example the clojure data structures would return true, whereas native java data structures would not:
(coll? {:a 1}) true (coll? (java.util.HashMap.)) false If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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