From 38343d7ec038093fde69199d966f5aed8f65412d Mon Sep 17 00:00:00 2001
From: rowan <rowan@kitsu.cafe>
Date: Wed, 9 Apr 2025 23:17:38 -0500
Subject: [PATCH] split monad law tests, add setoid to Option and Result

---
 src/algebra/option.js |  6 ++---
 src/algebra/result.js |  6 ++---
 tests/units/monad.js  | 58 +++++++++++++++++++++++++++++++++++--------
 3 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/src/algebra/option.js b/src/algebra/option.js
index 394e63c..945431d 100644
--- a/src/algebra/option.js
+++ b/src/algebra/option.js
@@ -1,9 +1,9 @@
-import { Algebra, Foldable, Monad, Monoid } from './interfaces.js'
+import { Algebra, Foldable, Monad, Monoid, Setoid } from './interfaces.js'
 
 /** @import { Morphism } from './types.js' */
 
 /** @template T */
-export class Some extends Algebra(Monoid, Monad, Foldable) {
+export class Some extends Algebra(Setoid, Monoid, Monad, Foldable) {
   /** @type {T} */
   #value
 
@@ -71,7 +71,7 @@ export class Some extends Algebra(Monoid, Monad, Foldable) {
 }
 
 /** @template T */
-export class None extends Algebra(Monoid, Monad, Foldable) {
+export class None extends Algebra(Setoid, Monoid, Monad, Foldable) {
   equals(other) {
     return other === none
   }
diff --git a/src/algebra/result.js b/src/algebra/result.js
index f31e1b5..16ce285 100644
--- a/src/algebra/result.js
+++ b/src/algebra/result.js
@@ -1,11 +1,11 @@
-import { Algebra, Foldable, Functor, Monad } from './interfaces.js'
+import { Algebra, Foldable, Functor, Monad, Setoid } from './interfaces.js'
 
 /** @import { Morphism } from './types.js' */
 
 /**
  * @template T, E
  */
-export class Ok extends Algebra(Monad, Foldable) {
+export class Ok extends Algebra(Setoid, Monad, Foldable) {
   /** @type {T} */
   #value
 
@@ -83,7 +83,7 @@ export class Ok extends Algebra(Monad, Foldable) {
 /**
  * @template T, E
  */
-export class Err extends Algebra(Functor, Monad) {
+export class Err extends Algebra(Setoid, Functor, Monad) {
   /** @type {E} */
   #value
 
diff --git a/tests/units/monad.js b/tests/units/monad.js
index d54178b..e052733 100644
--- a/tests/units/monad.js
+++ b/tests/units/monad.js
@@ -1,6 +1,8 @@
 import { it, assert } from 'folktest'
 import { Option, Result } from '../../src/index.js'
 
+const Monads = [Option, Result]
+
 const leftIdentity = (M, a, f) => {
   assert(M(a).chain(f).equals(f(a)))
 }
@@ -19,17 +21,53 @@ export const prove = (M, m, a, f, g) => {
   associativity(m, f, g)
 }
 
-export const Tests = [
-  it('should adhere to monadic laws', () => {
-    [Option, Result].forEach(F => {
-      const Ctr = F.of
+const inc = F => x => F.of(x + 1)
+const dbl = F => x => F.of(x * 2)
 
-      prove(
-        Ctr,
-        Ctr(1),
-        1,
-        x => Ctr(x + 1),
-        x => Ctr(x * 2)
+export const Tests = [
+  it('unit is a left identity', () => {
+    Monads.forEach(monad => {
+      const f = inc(monad)
+      // NOTE: okay but like, shut up
+      // @ts-ignore
+      assert(monad.of(1).chain(f).equals(f(1)))
+    })
+    //prove(
+    //  Ctr, M
+    //  Ctr(1), m
+    //  1, a
+    //  x => Ctr(x + 1), f
+    //  x => Ctr(x * 2) g
+    //)
+  }),
+
+  it('unit is a right identity', () => {
+    Monads.forEach(monad => {
+      const m = monad.of(1)
+
+      assert(
+        // NOTE: i heard this one already
+        // @ts-ignore
+        m.chain(monad.of).equals(m)
+      )
+    })
+  }),
+
+  it('unit is associative', () => {
+    Monads.forEach(monad => {
+      const m = monad.of(1)
+      const f = inc(monad)
+      const g = dbl(monad)
+      console.log(m.chain(f))
+
+      // NOTE: it was better the first time
+      // @ts-ignore
+      const x = m.chain(f).chain(g)
+      // @ts-ignore
+      const y = m.chain(x => f(x).chain(g))
+
+      assert(
+        x.equals(y)
       )
     })
   })