add support for collection expressions

LanguageExt.Core/CollectionBuilderAttribute.cs

@@ -0,0 +1,20 @@
+namespace System.Runtime.CompilerServices
+{
+    [AttributeUsage(
+        AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Interface,
+        Inherited = false,
+        AllowMultiple = false)]
+    public sealed class CollectionBuilderAttribute : Attribute
+    {
+        public CollectionBuilderAttribute(
+            Type builderType,
+            string methodName)
+        {
+            BuilderType = builderType;
+            MethodName = methodName;
+        }
+
+        public Type BuilderType { get; }
+        public string MethodName { get; }
+    }
+}

LanguageExt.Core/Immutable Collections/Arr/Arr.Module.cs

@@ -34,6 +34,17 @@ public static partial class Arr
         [Pure]
         public static Arr<T> create<T>(params T[] items) =>
             new Arr<T>(items);
+
+        /// <summary>
+        /// Create an array from a initial set of items
+        /// </summary>
+        /// <param name="items">Items</param>
+        /// <returns>Lst T</returns>
+        [Pure]
+        public static Arr<T> create<T>(
+            ReadOnlySpan<T> items) =>
+            create(
+                items.ToArray());
 
         /// <summary>
         /// Create an array from an initial set of items

LanguageExt.Core/Immutable Collections/Arr/Arr.cs

@@ -2,6 +2,7 @@
 using System.Linq;
 using System.Collections;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Diagnostics.Contracts;
 using static LanguageExt.Prelude;
 using LanguageExt.TypeClasses;
@@ -17,6 +18,9 @@ namespace LanguageExt
     /// for large arrays.
     /// </summary>
     /// <typeparam name="A">Value type</typeparam>
+    [CollectionBuilderAttribute(
+        typeof(Arr),
+        nameof(Arr.create))] 
     [Serializable]
     public struct Arr<A> :
         IEnumerable<A>,
@@ -721,6 +725,5 @@ public Arr<B> Bind<B>(Func<A, Arr<B>> f)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static implicit operator Arr<A>(SeqEmpty _) =>
             Empty;
-
     }
 }

LanguageExt.Core/Immutable Collections/List/Lst.Module.cs

@@ -50,6 +50,17 @@ public static partial class List
         public static Lst<T> create<T>(params T[] items) =>
             new Lst<T>(items);
 
+        /// <summary>
+        /// Create an array from a initial set of items
+        /// </summary>
+        /// <param name="items">Items</param>
+        /// <returns>Lst T</returns>
+        [Pure]
+        public static Lst<T> create<T>(
+            ReadOnlySpan<T> items) =>
+            create(
+                items.ToArray());
+
         /// <summary>
         /// Create a list from an initial set of items
         /// </summary>

LanguageExt.Core/Immutable Collections/List/Lst.cs

@@ -15,6 +15,9 @@ namespace LanguageExt
     /// Immutable list
     /// </summary>
     /// <typeparam name="A">Value type</typeparam>
+    [CollectionBuilder(
+        typeof(List),
+        nameof(List.create))]
     [Serializable]
     public readonly struct Lst<A> :
         IComparable<Lst<A>>,

LanguageExt.Core/Immutable Collections/Seq/Seq.Module.cs

@@ -57,6 +57,17 @@ public static Seq<A> create<A>(params A[] items)
             System.Array.Copy(items, nitems, items.Length);
             return FromArray(items);
         }
+
+        /// <summary>
+        /// Create an array from a initial set of items
+        /// </summary>
+        /// <param name="items">Items</param>
+        /// <returns>Lst T</returns>
+        [Pure]
+        public static Seq<T> create<T>(
+            ReadOnlySpan<T> items) =>
+            create(
+                items.ToArray());
 
         /// <summary>
         /// Create a sequence from an initial set of items

LanguageExt.Core/Immutable Collections/Seq/Seq.cs

@@ -17,6 +17,9 @@ namespace LanguageExt
     /// </summary>
     /// <typeparam name="A">Type of the values in the sequence</typeparam>
 
+    [CollectionBuilder(
+        typeof(Seq),
+        nameof(Seq.create))]
     public readonly struct Seq<A> :
 #pragma warning disable CS0618 // Remove ISeq complaint
         ISeq<A>,

LanguageExt.Core/Immutable Collections/Set/Set.Module.cs

@@ -32,6 +32,16 @@ public static partial class Set
         public static Set<T> create<T>() =>
             Set<T>.Empty;
 
+        /// <summary>
+        /// Create an array from a initial set of items
+        /// </summary>
+        /// <param name="items">Items</param>
+        /// <returns>Lst T</returns>
+        [Pure]
+        public static Set<T> create<T>(
+            ReadOnlySpan<T> items) =>
+            new Set<T>(items.ToArray());
+
         /// <summary>
         /// Create a new set pre-populated with the items in range
         /// </summary>

LanguageExt.Core/Immutable Collections/Set/Set.cs

@@ -19,6 +19,9 @@ namespace LanguageExt
     /// [wikipedia.org/wiki/AVL_tree](http://en.wikipedia.org/wiki/AVL_tree)
     /// </summary>
     /// <typeparam name="A">Set item type</typeparam>
+    [CollectionBuilder(
+        typeof(Set),
+        nameof(Set.create))]
     [Serializable]
     public readonly struct Set<A> :
         IEnumerable<A>,