How to use cases in Clojure

The conditional branching in Clojure can be performed using the case multi-way branch statement. Typically, it is used to cope with multiple and distinct conditions.

The syntax of the case statement is given below:

case expression/variable
     value1  statement1
     value2  statement2
     valueN  statementN
     statement ; default

It works as follows:

  • The given expression is evaluated into a single value (a.k.a., the expression's value).

  • The expression's value is compared against each value passed in the case statement. When matching, the subsequent statement gets executed.

  • If the expression's value did not match any of the case values, then the default statement is executed, the one with no value.

  • When no default expression is provided, and the expression's value did not match any case value, an error IllegalArgumentException is thrown.

The following diagram illustrates the flow of the case statement:

The case flow
The case flow

Code example

The following example demonstrates the use of the case statement:

(defn CaseExample []
   (def agelimit 18) 
   (case agelimit
      1  (println "Baby")   
      3  (println "Toddler")
      5  (println "Preschooler")
      10 (println "Gradeschooler")
      18 (println "Teen") 
      (println "Adult")
     ))
;;Call the function
(CaseExample)

Code explanation

Let's now explain the above code snippet:

  • Line 1: We define a private function called CaseExample.

  • Line 2: We initialize the variable ageLimit to 18.

  • Lines 3–9: We declare a case clause that evaluates the agelimit variable and specify a default statement that gets executed if the agelimit did not match any of the designated values.

  • Line 12: We invoke the CaseExample function.

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