diff --git a/src/algebra/free.js b/src/algebra/free.js
index bb68f07..be54b1e 100644
--- a/src/algebra/free.js
+++ b/src/algebra/free.js
@@ -1,5 +1,5 @@
 import { liftF } from './fn.js'
-import { Algebra, BaseSet, Comonad, Monad } from './index.js'
+import { Algebra, BaseSet, Monad, Semigroupoid } from './index.js'
 
 /** @import { InferredMorphism, Morphism } from './types.js' */
 
@@ -8,7 +8,7 @@ import { Algebra, BaseSet, Comonad, Monad } from './index.js'
  * @extends BaseSet
  * @mixes Monad
  */
-export class Suspend extends Algebra(Monad) {
+export class Suspend extends Algebra(Semigroupoid, Monad) {
   _value
   #fn
 
@@ -55,6 +55,14 @@ export class Suspend extends Algebra(Monad) {
     return this.map(g)
   }
 
+  /**
+   * @template T
+   * @param {InferredMorphism<T>} other 
+   */
+  compose(other) {
+    return this.chain(() => other)
+  }
+
   step() {
     return this.#fn(this._value)
   }
@@ -65,7 +73,7 @@ export class Suspend extends Algebra(Monad) {
 }
 
 /** @template T */
-export class Pure extends Algebra(Monad, Comonad) {
+export class Pure extends Algebra(Monad) {
   _value
 
   /** @param {T} value */
@@ -95,7 +103,7 @@ export class Pure extends Algebra(Monad, Comonad) {
    * @returns {Pure<U>}
    */
   map(f) {
-    return this.chain(x => new Pure(f(x)))
+    return this.chain(x => pure(f(x)))
   }
 
   /**
@@ -107,8 +115,12 @@ export class Pure extends Algebra(Monad, Comonad) {
     return this.map(f)
   }
 
-  extract() {
-    return this._value
+  /**
+   * @template T
+   * @param {InferredMorphism<T>} other 
+   */
+  compose(other) {
+    return this.chain(() => pure(other))
   }
 
   step() {
diff --git a/src/algebra/list.js b/src/algebra/list.js
index e23dd0a..4b8c83c 100644
--- a/src/algebra/list.js
+++ b/src/algebra/list.js
@@ -1,7 +1,7 @@
 import { concat } from '../iter.js'
 import { liftF } from './fn.js'
 import { Pure, Suspend } from './free.js'
-import { AlgebraWithBase, Comonad, Foldable } from './index.js'
+import { AlgebraWithBase, Category, Comonad, Foldable, Monoid } from './index.js'
 
 /** @import { InferredMorphism } from './types.js' */
 
@@ -11,7 +11,15 @@ const Nil = Symbol('Nil')
  * @template T
  * @extends {Pure<T>}
  */
-class ListPure extends AlgebraWithBase(Pure)(Foldable) {
+class ListPure extends AlgebraWithBase(Pure)(Category, Foldable, Monoid) {
+  static empty() {
+    return List.empty()
+  }
+
+  static id() {
+    return List.empty()
+  }
+
   head() {
     return this._value
   }
@@ -35,7 +43,7 @@ class ListPure extends AlgebraWithBase(Pure)(Foldable) {
  * @template T
  * @extends {Suspend<T>}
  */
-class ListSuspend extends AlgebraWithBase(Suspend)(Foldable, Comonad) {
+class ListSuspend extends AlgebraWithBase(Suspend)(Foldable, Monoid, Comonad) {
   /**
    * @param {Iterator<T>} iter
    */
@@ -79,6 +87,10 @@ class ListSuspend extends AlgebraWithBase(Suspend)(Foldable, Comonad) {
   extract() {
     return this.reduce(reduceArray, [])
   }
+
+  static empty() {
+    return List.empty()
+  }
 }
 
 /**
@@ -120,9 +132,3 @@ const Empty = new ListPure(Nil)
  */
 const reduceArray = (acc, value) => acc.concat(value)
 
-
-const a = Array.from({ length: 10 }).map((_, i) => i)
-
-const wawa = List.from(a)
-console.log(wawa.reduce((acc, value) => acc.concat(value), []))
-
diff --git a/src/algebra/option.js b/src/algebra/option.js
index 96158a5..42d729b 100644
--- a/src/algebra/option.js
+++ b/src/algebra/option.js
@@ -1,9 +1,9 @@
-import { Algebra, Foldable, Functor, Monad } from './index.js'
+import { Algebra, Foldable, Monad, Monoid } from './index.js'
 
 /** @import { Morphism } from './types.js' */
 
 /** @template T */
-export class Some extends Algebra(Monad, Foldable) {
+export class Some extends Algebra(Monoid, Monad, Foldable) {
   /** @type {T} */
   #value
 
@@ -59,10 +59,14 @@ export class Some extends Algebra(Monad, Foldable) {
   reduce(f, init) {
     return f(init, this.#value)
   }
+
+  empty() {
+    return Option.empty()
+  }
 }
 
 /** @template T */
-class None extends Algebra(Monad, Foldable) {
+class None extends Algebra(Monoid, Monad, Foldable) {
   /**
    * @template R
    * @param {Morphism<T, R>} _f
@@ -99,6 +103,10 @@ class None extends Algebra(Monad, Foldable) {
   reduce(_f, init) {
     return init
   }
+
+  empty() {
+    return Option.empty()
+  }
 }
 
 /**
@@ -113,6 +121,10 @@ export class Option {
   static of(value) {
     return Some.of(value)
   }
+
+  static empty() {
+    return none
+  }
 }
 
 /**
diff --git a/src/algebra/reader.js b/src/algebra/reader.js
new file mode 100644
index 0000000..16448b8
--- /dev/null
+++ b/src/algebra/reader.js
@@ -0,0 +1,71 @@
+import { id } from './fn.js'
+import { Algebra, Monad } from './index.js'
+
+/** @import { InferredMorphism } from './types.js' */
+
+/**
+ * @template T
+ * @typedef {InferredMorphism<T>} ReaderFn
+ */
+
+/** @template T */
+export class Reader extends Algebra(Monad) {
+  #run
+
+  /**
+   * @param {InferredMorphism<T>} run 
+   */
+  constructor(run) {
+    super()
+
+    this.#run = run
+  }
+
+  /**
+   * @template T
+   * @param {T} a
+   * @returns {Reader<T>}
+   */
+  static of(a) {
+    return new Reader(/** @type {InferredMorphism<T>} */(_env => a))
+  }
+
+  /** @template T */
+  static ask() {
+    return new Reader(/** @type {InferredMorphism<T>} */(id))
+  }
+
+  /**
+   * @param {InferredMorphism<T>} f 
+   * @returns {Reader<T>}
+   */
+  map(f) {
+    return new Reader(/** @type {InferredMorphism<T>} */(env => f(this.#run(env))))
+  }
+
+  /**
+   * @param {InferredMorphism<T>} f 
+   * @returns {Reader<T>}
+   */
+  chain(f) {
+    return new Reader(env => f(this.#run(env)).run(env))
+  }
+
+  /**
+   * @param {InferredMorphism<T>} f 
+   * @returns {Reader<T>}
+   */
+  local(f) {
+    return new Reader(/** @type {InferredMorphism<T>} */(env => this.#run(f(env))))
+  }
+
+  /**
+   * @template R
+   * @param {T} env 
+   * @returns {R}
+   */
+  run(env) {
+    return this.#run(env)
+  }
+}
+
diff --git a/src/algebra/result.js b/src/algebra/result.js
index 833be79..14a4f6c 100644
--- a/src/algebra/result.js
+++ b/src/algebra/result.js
@@ -15,6 +15,7 @@ export class Ok extends Algebra(Monad, Foldable) {
    */
   constructor(value) {
     super()
+
     this.#value = value
   }