by @yokolet

Level: easy

Conditional case

The case macro is a similar conditional to cond/condp. It branches to multiple clauses. The difference is that case doesn’t evaluate branching expressions. In case, it should be a constant. What we can do with case looks like map (data structure).

The syntax is: (case e & clauses)

user> (defn cases-to-do
        [temp]
        (case temp
          :65-80 "I'll enjoy walking at a park."
          :45-64 "I'll spend time at a cafe."
          "I'll curl up in my bed"))
#'user/cases-to-do
user> (cases-to-do :65-80)
"I'll enjoy walking at a park."
user> (cases-to-do :45-64)
"I'll spend time at a cafe."
user> (cases-to-do :30)
"I'll curl up in my bed"
user> (cases-to-do :100) ; also falls to default
"I'll curl up in my bed"

user> ; if we use map...
user> (def my-cases {:64-80 "I'll enjoy walking at a park."
                     :45-64 "I'll spend time at a cafe."
                     :other "I'll curl up in my bed"})
#'user/my-cases
user> (my-cases :64-80)
"I'll enjoy walking at a park."
user> (my-cases :45-64)
"I'll spend time at a cafe."
user> (my-cases :other)
"I'll curl up in my bed"
user> (my-cases :30) ; hash-map can't take a key that doesn't match anything
nil

References