Ord semilattice example

examples/ord/Ord.test.ts

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+import * as TL from './Ord'
+import * as fc from 'fast-check'
+
+const trafficLightArb: fc.Arbitrary<TL.TrafficLight> = fc.oneof(
+  fc.constant(TL.red),
+  fc.constant(TL.yellow),
+  fc.constant(TL.yellowFlashing),
+  fc.constant(TL.green)
+)
+
+describe('properties', () => {
+  // the "zero" is always the lowest so does nothing
+  it('a + zero == a', () => {
+    fc.assert(
+      fc.property(
+        trafficLightArb,
+        (tl) =>
+          TL.trafficLightJoin.join(tl, TL.trafficLightJoin.zero) ===
+          tl
+      )
+    )
+  })
+
+  it('a + green == green', () => {
+    fc.assert(
+      fc.property(
+        trafficLightArb,
+        (tl) => TL.trafficLightJoin.join(tl, TL.green) === TL.green
+      )
+    )
+  })
+
+  it('a + b == b + a', () => {
+    fc.assert(
+      fc.property(
+        trafficLightArb,
+        trafficLightArb,
+        (tlA, tlB) =>
+          TL.trafficLightJoin.join(tlA, tlB) ===
+          TL.trafficLightJoin.join(tlB, tlA)
+      )
+    )
+  })
+
+  it('a + (b + c) == (a + b) + c', () => {
+    fc.assert(
+      fc.property(
+        trafficLightArb,
+        trafficLightArb,
+        trafficLightArb,
+        (tlA, tlB, tlC) =>
+          TL.trafficLightJoin.join(
+            tlA,
+            TL.trafficLightJoin.join(tlB, tlC)
+          ) ===
+          TL.trafficLightJoin.join(
+            TL.trafficLightJoin.join(tlA, tlB),
+            tlC
+          )
+      )
+    )
+  })
+
+  it('a + a == a', () => {
+    fc.assert(
+      fc.property(
+        trafficLightArb,
+        (tlA) => TL.trafficLightJoin.join(tlA, tlA) === tlA
+      )
+    )
+  })
+
+  it('a + b + b == a + b', () => {
+    fc.assert(
+      fc.property(
+        trafficLightArb,
+        trafficLightArb,
+        (tlA, tlB) =>
+          TL.trafficLightJoin.join(tlA, tlB) ===
+          TL.trafficLightJoin.join(
+            TL.trafficLightJoin.join(tlA, tlB),
+            tlB
+          )
+      )
+    )
+  })
+})

examples/ord/Ord.ts

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+import * as BJS from 'fp-ts/BoundedJoinSemilattice'
+import * as Ord from 'fp-ts/Ord'
+import { Ord as numOrd } from 'fp-ts/number'
+
+const mk = <A>(a: A) => a
+
+export const red = mk<TrafficLight>('red')
+export const yellow = mk<TrafficLight>('yellow')
+export const yellowFlashing = mk<TrafficLight>('yellow-flashing')
+export const green = mk<TrafficLight>('green')
+
+export type TrafficLight =
+  | 'red'
+  | 'yellow'
+  | 'yellow-flashing'
+  | 'green'
+
+const tlNums: Record<TrafficLight, number> = {
+  red: 0,
+  yellow: 1,
+  'yellow-flashing': 2,
+  green: 3,
+}
+
+const trafficLightOrd: Ord.Ord<TrafficLight> = {
+  equals: (a, b) => numOrd.equals(tlNums[a], tlNums[b]),
+  compare: (a, b) => numOrd.compare(tlNums[a], tlNums[b]),
+}
+
+export const trafficLightJoin: BJS.BoundedJoinSemilattice<TrafficLight> = {
+  join: Ord.max(trafficLightOrd),
+  zero: 'red',
+}