def & names in Clojure

Names a market stall's inventory with def, deriving one value from the others.

;; def interns a name in the namespace; names use hyphens, not camelCase
(def stall-name "Ridgeline Orchard")
(def crates-on-hand 12)
(def apples-per-crate 40)

;; a def can be computed from names defined above it
(def apples-on-hand (* crates-on-hand apples-per-crate))

;; a trailing ? marks a name that answers yes or no
(def restock-needed? (< crates-on-hand 15))

;; a trailing ! marks a name tied to something that changes
(def sold-today! (atom 0))
(swap! sold-today! + 96)

(println stall-name "has" apples-on-hand "apples")
(println "restock?" restock-needed? "- sold" @sold-today!)

How it works

1. (def stall-name "Ridgeline Orchard") interns a name in the namespace, hyphenated rather than camelCase.
2. apples-on-hand is computed as (* crates-on-hand apples-per-crate) from the two defs above it.
3. restock-needed? ends in a question mark for a yes-or-no value, and sold-today! in a bang for the atom that swap! updates.

Keywords and builtins used here

• atom
• def
• println

The run, in numbers

Lines

17

Characters to type

591

Tokens

66

Three-star pace

75 tpm

At the three-star pace of 75 tokens a minute, this run takes about 53 seconds.

Type this snippet

Step 1 of 3 in Values & bindings, step 1 of 27 in Language basics.

Next →