JS to CLJS # 3
I’ll regularly take a JavaScript problem and work it out in ClojureScript. This will hopefully take away some of the Magic™ of functional programming and show how to solve real problems. I promise you won’t have to learn what a monad is.
Problem
Write a function that takes a list of pairs and classifies them as valid or invalid. Pairs are valid if the age is over 35 and the signature is true.
Example input:
[[18, true],[45, true],[61, false],[37, false],[21, false],[78, true]]For example:
valid([[18, true],[45, true],[61, false],[37, false],[21, false],[78, true]]) ===
["Invalid", "Valid", "Invalid", "Invalid", "Invalid", "Valid"]Solutions
;;#cljs
(defn valid? [data]
(map (fn [[age signed?]]
(if (and (> age 35) signed?)
"Valid"
"Invalid"))
data))Thoughts
Mostly straightforward:
- We destructure each
age/signed?pair. Such destructuring is a normal occurrence. - We return a lazy sequence via
map. We could do something like “get the first three ‘Valid’” and the calculations would stop as soon as we found them.
This is clearly a tutorial type problem, but I suggest getting into the habit of using more descriptive data structures:
;;#cljs
(defn valid? [data]
(map (fn [{:keys [:age :signed?] :as person}]
(assoc person :valid? (and (> age 35) signed?)))
data))
(valid? [{:age 18 :signed? true}
{:age 45 :signed? true}
{:age 61 :signed? false}
{:age 37 :signed? false}
{:age 21 :signed? false}
{:age 78 :signed? true}])
=> ({:age 18 :signed? true :valid? false}
{:age 45 :signed? true :valid? true}
{:age 61 :signed? false :valid? false}
{:age 37 :signed? false :valid? false}
{:age 21 :signed? false :valid? false}
{:age 78 :signed? true :valid? true})I’m partially anticipating that this function will be part of a larger data-flow, so the return is transformed data instead of just the valid? data apart from the context.