Signum Documentation

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The most simple immutable data structure, can be used as a stack or as a list, if you are not planning to insert elements in the middle (or the end).

Internally is just an immutable linked list of nodes, where each node has one value and a link to the next. So Push, Pop and Peak are all O(1).

public class ImmutableStack<T>: IEnumerable<T>
   public static ImmutableStack<T> Empty { get; } //The only way to get a Empty immutable stack. 

   public bool IsEmpty { get; } //returns true if the current instance is empty.
   public ImmutableStack<T> Push(T value) //Creates a new immutable stack with value pushed in the head
   public ImmutableStack<T> Pop() //returns a new stack without the head
   public T Peek() //returns the element in the head
   public virtual IEnumerator<T> GetEnumerator()
   public override string ToString()

public static class ImmutableStackExtensions
    //Reverse the order of elements
    //Stack: [3]->[2]->[1]->[]
    //Result: [1]->[2]->[3]->[]
    public static ImmutableStack<T> Reverse<T>(this ImmutableStack<T> stack); 

    //Reverse the order of elements and concatenates it with initial.
    //Stack: [3]->[2]->[1]->[]
    //Initial: [4]->[]
    //Result: [1]->[2]->[3]->[4]->[]
    public static ImmutableStack<T> Reverse<T>(this ImmutableStack<T> stack, ImmutableStack<T> initial);

Also, since ImmutableStack implements IEnumerable, all the Linq extension methods are applicable.


ImmutableStack<int> stack = ImmutableStack<int>.Empty;

for (int i = 0; i < 10; i++)
    stack = stack.Push(i);

//Writes: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

while (!stack.IsEmpty)
    stack = stack.Pop();
//Writes: 9876543210

//Writes: []