54 lines
2.7 KiB
Markdown
54 lines
2.7 KiB
Markdown
---
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title: Clojure Create Local Variables with Let
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---
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`let` is a fundamental part of Clojure. Whereas `def` creates a global variable, `let` creates a local variable.
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(def x 5)
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(println x)
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; => 5
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; nil
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(let [x 2]
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(println x))
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; => 2
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; nil
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(println x)
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; => 5
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; nil
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 <a href='https://ideone.com/xcNth2' target='_blank' rel='nofollow'>IDEOne it!</a>
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`x` in this example never actually gets changed. `x` just refers to something different inside of our `let` binding. This can be a useful way to avoid repetition inside a function.
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This is incredibly useful. Having too many global variables can lead to nasty bugs and unintended behaviour.
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(def x 5)
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(defn add-5 [y] (+ x y))
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(add-5 5)
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; => 10
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(defn change-x []
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(def x 6))
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(change-x)
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; => nil
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(add-5 5)
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; => 11
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 <a href='https://ideone.com/MFjA3C' target='_blank' rel='nofollow'>IDEOne it!</a>
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Uh oh! That's not adding 5 anymore! Of course, this example is a bit silly, but using too many global variables can lead to bugs that are just as scary as this one.
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**Note:** We aren't really _reassigning_ `x` here, like you would in a C-like language. We're just creating a new variable that happens to also be called x. This is a _very, very, **very**_ bad idea.
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## Multiple Bindings
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`let` can also define multiple variables at once, and can assign variables to expressions.
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(let [spam "foo"
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ham (str "b" "ar")] ; str is a function that concatenates strings
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(println spam ham)) ; or converts variables into strings.
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; => foo bar
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; nil
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 <a href='https://ideone.com/y5EBIM' target='_blank' rel='nofollow'>IDEOne it!</a>
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| [ Previous](//forum.freecodecamp.com/t/clojure-conditionals/18412) | [ Home ](//forum.freecodecamp.com/t/clojure-resources/18422) | [Next ](//forum.freecodecamp.com/t/clojure-loop-recur/18418)|
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| [Conditionals](//forum.freecodecamp.com/t/clojure-conditionals/18412) | [Table of Contents](//forum.freecodecamp.com/t/clojure-resources/18422) | [Loop and Recur](//forum.freecodecamp.com/t/clojure-loop-recur/18418)| |