finished list

src/algebra/fn.js

@@ -1,5 +1,5 @@
 import { curry } from '../curry.js'
-import { Free, Suspend, suspend, pure } from './free.js'
+import { Suspend, suspend, pure } from './free.js'
 
 /** @import {InferredMorphism, Morphism, ChainConstructor} from './types.js' */
 
@@ -42,4 +42,3 @@ export const liftF = x => suspend(
   /** @type {InferredMorphism<T>} */(pure)
 )
 
-

src/algebra/list.js

@@ -1,3 +1,4 @@
+import { concat } from '../iter.js'
 import { liftF } from './fn.js'
 import { Pure, Suspend } from './free.js'
 import { AlgebraWithBase, Comonad, Foldable } from './index.js'
@@ -12,7 +13,7 @@ const Nil = Symbol('Nil')
  */
 class ListPure extends AlgebraWithBase(Pure)(Foldable) {
   head() {
-    return this.head
+    return this._value
   }
 
   tail() {
@@ -30,14 +31,13 @@ class ListPure extends AlgebraWithBase(Pure)(Foldable) {
   }
 }
 
-
 /**
  * @template T
  * @extends {Suspend<T>}
  */
 class ListSuspend extends AlgebraWithBase(Suspend)(Foldable, Comonad) {
   /**
-   * @param {IteratorObject<T>} iter
+   * @param {Iterator<T>} iter
    */
   constructor(iter) {
     const next = iter.next()
@@ -47,6 +47,16 @@ class ListSuspend extends AlgebraWithBase(Suspend)(Foldable, Comonad) {
     super(value, fn)
   }
 
+  /**
+   * @template {Iterable<T>} T
+   * @this {ListSuspend<Iterator<T>>}
+   * @param {Iterator<T>} value 
+   * @returns {ListSuspend<T>}
+   */
+  cons(value) {
+    return new ListSuspend(concat(value, this._value))
+  }
+
   head() {
     return this._value
   }
@@ -67,7 +77,7 @@ class ListSuspend extends AlgebraWithBase(Suspend)(Foldable, Comonad) {
   }
 
   extract() {
-    return this.reduce((acc, value) => acc.concat(value), [])
+    return this.reduce(reduceArray, [])
   }
 }
 
@@ -102,8 +112,16 @@ export class List {
 
 const Empty = new ListPure(Nil)
 
+/**
+ * @template T
+ * @param {T[]} acc
+ * @param {T} value
+ * @returns {T[]}
+ */
+const reduceArray = (acc, value) => acc.concat(value)
 
-const a = Array.from({ length: 100 }).map((_, i) => i)
+
+const a = Array.from({ length: 10 }).map((_, i) => i)
 
 const wawa = List.from(a)
 console.log(wawa.reduce((acc, value) => acc.concat(value), []))

src/iter.js

@@ -0,0 +1,34 @@
+/**
+ * @template T
+ * @param {T | Iterable<T> | Iterator<T>} value
+ * @returns {value is Iterable<T>}
+ */
+export function isIterable(value) {
+  return value[Symbol.iterator] != null
+}
+/**
+ * @template T
+ * @param {T | Iterable<T> | Iterator<T>} value 
+ * @yields {T}
+ */
+export function* iter(value) {
+  if (isIterable(value)) {
+    yield* Iterator.from(value)
+  } else {
+    yield value
+  }
+}
+
+/**
+ * @template T
+ * @param {...(Iterable<T> | Iterator<T>)} iterators
+ * @yields {T}
+ */
+export const concat = function*(...iterators) {
+  for (const iter of iterators) {
+    for (const item of Iterator.from(iter)) {
+      yield item
+    }
+  }
+}
+