How to evaluate a sequence of impure functions in Clojure?

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没有蜡笔的小新
没有蜡笔的小新 2021-01-17 13:09

How can I evaluate a list of (impure) functions in Clojure? For instance:

[#(println \"1\") #(println \"2\") #(println \"3\")]

The expected

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  •  无人及你
    2021-01-17 13:44

    This will eagerly consume the whole seq, calling all functions for side effects and returning whatever the last one returns:

    (reduce #(%2) nil [#(println :foo) #(println :bar)])
    ; => prints :foo, then :bar, then returns nil
    

    If you want to hold onto the return values, you can use reductions instead:

    (reductions #(%2) nil [#(println :foo) #(println :bar)])
    ; => prints :foo, then :bar, then returns (nil nil)
    

    reductions is found in clojure.contrib.seq-utils in Clojure 1.1 and in clojure.core in current snapshots of 1.2.

    Update: Note that reductions returns a lazy seq, so it's no improvement over map (NB. in map you'd want to use #(%) rather than #(%2)). I mentioned it here mostly for completeness. In fact, I posted the whole answer for completeness, because normally I'd go with the doseq approach (see Brian's answer).

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