Creating Lazy stream in CSharp

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Hand-Toss a Stream
(Lazy List)
in C#
Dhaval Dalal
https://dhavaldalal.wordpress.com
@softwareartisan

Implementing Lazy List
IEnumerable<int> Naturals(int @from) { 
for (var i = @from; true ; i++) { 
yield return i; 
} 
} 
N...

Implementing Lazy List

Using Lambda
Wrap the tail of the
list in a closure.
1 ?
Implementing Lazy List

Using Lambda
Wrap the tail of the
list in a closure.
When we need the result
evaluate the tail by
invoking the closure.
Ev...

Using Lambda
Wrap the tail of the
list in a closure.
When we need the result
evaluate the tail by
invoking the closure.
Ad...

Using Lambda
Wrap the tail of the
list in a closure.
When we need the result
evaluate the tail by
invoking the closure.
Ad...

Immutable Stream with
eager Head & lazy Tail
sealed class Stream<T> { 
private readonly T head; 
private readonly Func<Str...

Immutable Stream with
eager Head & lazy Tail
sealed class Stream<T> { 
private readonly T head; 
private readonly Lazy<Str...

Immutable Stream with
eager Head & lazy Tail
var empty = new Stream<int>(0, null); 
Console.WriteLine(empty); // Stream<Sy...

Introduce Empty Stream
sealed class Stream<T> { 
public static readonly Stream<T> Empty
= new Stream<T>(default(T), null);...

Introduce Empty Stream
var empty = Stream<int>.Empty; 
Console.WriteLine(empty); // Empty 
Console.WriteLine(empty.IsEmpty...

Doing Side-effects
sealed class Stream<T> {
…
… 
public void ForEach(Action<T> action) { 
if (IsEmpty) 
return;
 
action(H...

Consing to Stream
sealed class Stream<T> { 
…
… 
// Cons using + 
public static Stream<T> operator + (Stream<T> s, T eleme...

Append to Stream
sealed class Stream<T> {
… 
// Append using + 
public static Stream<T> operator + (T element, Stream<T> s...

sealed class Stream<T> {
…
public static Stream<R> Of<R>(params R[] rs) { 
var stream = Stream<R>.Empty; 
var indices = rs...

Concat another Stream
sealed class Stream<T> { 
… 
public static Stream<T> operator + (Stream<T> @this,
Stream<T> other) {...

sealed class Stream<T> { 
…
public Stream<T> Take(int howMany) { 
if (IsEmpty || howMany <= 0) 
return Stream<T>.Empty; 
 ...

sealed class Stream<T> { 
…
public Stream<T> Drop(int howMany) { 
if (IsEmpty || howMany <= 0) 
return this; 
 
return Tai...

sealed class Stream<T> { 
…
…
public static Stream<R> Generate<R>(Func<R> fn) =>  
new Stream<R>(fn(), new Lazy<Stream<R>>...

sealed class Stream<T> { 
…
…
public static Stream<R> Iterate<R>(R initial, Func<R, R> fn) =>  
new Stream<R>(initial,
new...

sealed class Stream<T> { 
…
…
public void Deconstruct(out T first, out Stream<T> rest) { 
if (IsEmpty)  
throw new Argumen...

sealed class Stream<T> { 
…
public void Deconstruct(out T first, out Stream<T> rest) { 
if (IsEmpty)  
throw new ArgumentE...

sealed class Stream<T> { 
…
public void Deconstruct(out T first, out T second,
out Stream<T> rest) => 
(first, (second, re...

Transform each element
sealed class Stream<T> { 
…
… 
public Stream<R> Select<R>(Func<T, R> fn) { 
if (IsEmpty) 
return St...

Filtering the Stream
sealed class Stream<T> { 
… 
public Stream<T> Where(Predicate<T> pred) { 
if (IsEmpty) 
return Stream...

Flatmap the Stream
sealed class Stream<T> {
… 
public Stream<T> SelectMany(Func<T, Stream<R>> fn) { 
if (IsEmpty) 
return ...

Reverse
sealed class Stream<T> { 
…
… 
public Stream<T> Reverse() { 
Stream<T> Reverse0(Stream<T> acc, Stream<T> source) {...

Take while
predicate holds
sealed class Stream<T> { 
… 
public Stream<T> TakeWhile(Predicate<T> pred) { 
if (IsEmpty) 
ret...

sealed class Stream<T> { 
… 
public Stream<T> DropWhile(Predicate<T> pred) { 
if (IsEmpty) 
return Stream<T>.Empty; 
 
if ...

sealed class Stream<T> { 
… 
public U Aggregate<U>(U identity, Func<U, T, U> func) { 
if (IsEmpty) 
return identity; 
 
re...

sealed class Stream<T> { 
… 
public bool All(Predicate<T> pred) { 
bool All0(bool accumulator, Stream<T> stream) { 
if (st...

sealed class Stream<T> { 
… 
public bool Any(Predicate<T> pred) { 
bool Any0(bool accumulator, Stream<T> stream) { 
if (st...

sealed class Stream<T> { 
… 
public Stream<T> Scan(U identity, Func<U, T, U> func) { 
if (IsEmpty) 
return Stream<T>.Empty...

Zip two Streams
sealed class Stream<T> { 
… 
public Stream<(T,U)> Zip<U>(Stream<U> that) { 
if (this.IsEmpty || that.IsEmp...

Zip with function
sealed class Stream<T> { 
… 
public Stream<R> ZipWith<U, R>(Stream<U> that, Func<T, U, R> fn) { 
if (thi...

Splitsealed class Stream<T> { 
… 
public (Stream<T>, Stream<T>) Split(Predicate<T> pred) { 
(Stream<T>, Stream<T>) Split0(...

To List
sealed class Stream<T> { 
…
public List<T> ToList() { 
var result = new List<T>(); 
ForEach(result.Add); 
return r...

Find first 6 primes using the Sieve of
Eratosthenes
Hint: Use Stream created earlier
http://world.mathigon.org/Prime_Numbe...

Sieve
Stream<int> From(int start) =>
Stream<int>.Iterate(start, x => x + 1); 
Stream<int> Sieve(Stream<int> s) { 
var firs...

First 10 Fibonacci Nos.
Write a function fibonacci which consumes an
integer and produces that many numbers in the
fibonac...

IEnumerable<int> Fibonacci(int howMany) {
var (first, second) = (0, 1); 
for (var i = 0; i < howMany; i++) { 
yield return...

IEnumerable<int> Fibonacci(int howMany) {
return IEnumerableExtensions.Iterate<(int, int)>((0, 1), tuple => { 
var (first,...

First 10 Fibonacci Nos.
Using Stream
https://www.haskell.org/tutorial/functions.html
var seed = From(0).Take(2); 
// Start...

Prime Counts
Using Lazy Lists, write a
program that counts number of
primes up to a given number.
At every power of 10, it...

class Streams { 
public static Stream<int> Range(int start, int count) { 
if (count < 0) 
throw new ArgumentOutOfRangeExce...

Prime Counts Using Stream
Stream<(int, int)> PrimeCount(int howManyPowerOf10) { 
bool IsPrime(int x) => Streams.Range(2, x...

Prime Counts using IEnumerable
First, write our own Scan
static class IEnumerableExtensions {
public static IEnumerable<U>...

Prime Counts using IEnumerable
IEnumerable<(int, int)> PrimeCount(int howManyPowerOf10) { 
bool IsPrime(int x) => Enumerab...

Drawbacks of this
Stream Implementation
As C# compiler does not support Tail-
Recursion, all the APIs that are
implemented...

But still its a good
mental exercise to create
streams from first
principles!

Thank-you!

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