Comments on: Clojure: Checking for a nil value in a collection http://www.markhneedham.com/blog/2009/11/21/clojure-checking-for-a-nil-value-in-a-collection/ Thoughts on Software Development Wed, 17 Mar 2010 23:38:45 +0000 http://wordpress.org/?v=2.8.4 hourly 1 By: John Hume http://www.markhneedham.com/blog/2009/11/21/clojure-checking-for-a-nil-value-in-a-collection/comment-page-1/#comment-27083 John Hume Sun, 22 Nov 2009 17:26:53 +0000 http://www.markhneedham.com/blog/?p=1856#comment-27083 Oops ... clearly I haven't been writing enough Clojure recently. I stick by my assertion that `some` isn't a predicate, but it returns the first logically true result of applying the first argument (not the value that yielded the logical true, as I previously stated). Given this, it will always just return true or nil if you give it a true predicate function as the first argument. There are these though: (some #{:foo :bar} [:baz :bar]) => :bar (some {:a "Aye" :b "Bee"} [:c :b]) => "Bee" Oops … clearly I haven't been writing enough Clojure recently. I stick by my assertion that `some` isn't a predicate, but it returns the first logically true result of applying the first argument (not the value that yielded the logical true, as I previously stated). Given this, it will always just return true or nil if you give it a true predicate function as the first argument.

There are these though:

(some #{:foo :bar} [:baz :bar]) => :bar

(some {:a "Aye" :b "Bee"} [:c :b]) => "Bee"

]]> By: John Hume http://www.markhneedham.com/blog/2009/11/21/clojure-checking-for-a-nil-value-in-a-collection/comment-page-1/#comment-27082 John Hume Sun, 22 Nov 2009 17:14:16 +0000 http://www.markhneedham.com/blog/?p=1856#comment-27082 I don't think Clojure prefers nil over false. Note that it's `some`, not `some?`: it isn't a predicate for seeing whether something in the collection satisfies another predicate, rather it's a function for getting some element that satisfies a given predicate. (There is, however, no predicate for doing this job, while there are `every?`, `not-every?`, and `not-any?`, so it ends up used in place of a predicate often, thanks to nil being falsey.) I don't think Clojure prefers nil over false. Note that it's `some`, not `some?`: it isn't a predicate for seeing whether something in the collection satisfies another predicate, rather it's a function for getting some element that satisfies a given predicate. (There is, however, no predicate for doing this job, while there are `every?`, `not-every?`, and `not-any?`, so it ends up used in place of a predicate often, thanks to nil being falsey.)

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