[ACCEPTED]-When to use let vs. if-let in Clojure-clojure
I guess if-let should be used when you'd like 9 to reference an
if condition's value in the 8 "
then" part of the code:
i.e. instead 7 of
(let [result :foo] (if result (do-something-with result) (do-something-else)))
(if-let [result :foo] (do-something-with result) (do-something-else))
which is a little neater, and 6 saves you indenting a further level. As 5 far as efficiency goes, you can see that 4 the macro expansion doesn't add much overhead:
(clojure.core/let [temp__4804__auto__ :foo] (if temp__4804__auto__ (clojure.core/let [result temp__4804__auto__] (do-something-with result)) (do-something-else)))
This 3 also illustrates that the binding can't 2 be referred to in the "
else" part 1 of the code.
A good use case for
if-let is to remove the need 8 to use anaphora. For example, the Arc programming 7 language provides a macro called
aif that allows 6 you to bind a special variable named
it within 5 the body of an
if form when a given expression 4 evaluates to logical true. We can create 3 the same thing in Clojure:
(defmacro aif [expr & body] `(let [~'it ~expr] (if ~'it (do ~@body)))) (aif 42 (println it)) ; 42
This is fine and 2 good, except that anaphora do not nest, but 1
(aif 42 (aif 38 [it it])) ;=> [38 38] (aif 42 [it (aif 38 it)]) ;=> [42 38] (if-let [x 42] (if-let [y 38] [x y])) ;=> [42 38]
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