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comparison 6-Clojure/bearings.clj @ 83:eccc649d49a2

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Add Day 2 and Day 3 notes and example code Clojure STILL doesn't make much sense in lots of places
author IBBoard <dev@ibboard.co.uk>
date Sat, 08 Jun 2019 21:23:27 +0100
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82:cf7182bca068 83:eccc649d49a2
1 ; Based on Compass
2 (def directions [:north :east :south :west])
3
4 ; Define a "fixed movement" protocol - "m" is effectively "this"
5 (defprotocol FixedMovement
6 (direction [m]) ; Find your current direction
7 (left [m]) ; turn left one position
8 (right [m])) ; turn right one position
9
10 ; Define an implementation with a single field (not a parameter - although it's defined the same)
11 (defrecord CompassBearings [bearing]
12 ; Specify which protocol we're implementing
13 FixedMovement
14 ; And define the methods
15 (direction [_] (directions bearing)) ; Look-up our index in the list
16 ; Clojure uses immutable values, so these functions create new CompassBearing objects
17 (left [_] (CompassBearings. (mod (- bearing 1) (count directions)))) ; Create a new instance (ClassName.) with a value from rotating one slot left
18 (right [_] (CompassBearings. (mod (+ bearing 1) (count directions))))
19 ; And we can specify more
20 Object
21 (toString [this] (str "[" (direction this) "]")) ; Presumably we could also call (directions bearing) directly.
22 ; We have to pass something to (direction) because we're doing functions and so can't do "obj.function()" to keep the reference to what we're getting directions of.
23 )
24
25 ; Define a thing that has bearings - e.g. an actor in a scene
26 ; It'd be nice if we could do an automated default so that we're not passing in magic numbers
27 (def actor (CompassBearings. 0))
28 (println actor) ; Prints default internal format
29 (println (:bearing actor)) ; Access a field using the keyword as a function. Because keywords with meaning happen EVERYWHERE in Clojure!
30 (println (str actor)) ; Uses our toString method
31 (println (str (left actor)))
32 (println (str (right (right actor))))
33