Introducing Discard and using it to make a generic Apply function.

Funcky.Test/Extensions/FuncExtensions/ApplyTest.cs

@@ -0,0 +1,36 @@
+using static Funcky.Discard;
+
+namespace Funcky.Test.Extensions.FuncExtensions;
+
+public class ApplyTest
+{
+    [Fact]
+    public void Test()
+    {
+        var func = Linear0;
+
+        var f1 = ((Func<int, int, int, int>)Linear0).Apply(_, _, 10);
+        var f2 = func.Apply(2, _, 7);
+        var f3 = Funcky.Extensions.FuncExtensions.Apply<int, int, int, int>(Linear0, _, _, 42);
+
+        Assert.Equal(30, f1(10, 2));
+        Assert.Equal(72, f2(10));
+    }
+
+    [Fact]
+    public void Test2()
+    {
+    }
+
+    private static int Linear0(int a, int b, int c)
+        => a + (b * c);
+
+    private int Function(int x)
+    {
+        return _ switch
+        {
+            _ when x == 3 => 0,
+            _ => 1,
+        };
+    }
+}

Funcky/Extensions/FuncExtensions/Apply.cs

@@ -0,0 +1,22 @@
+namespace Funcky.Extensions;
+
+public static partial class FuncExtensions
+{
+    public static Func<T2, T3, TResult> Apply<T1, T2, T3, TResult>(this Func<T1, T2, T3, TResult> function, T1 arg1, Unit arg2, Unit arg3)
+        => (a2, a3) => function(arg1, a2, a3);
+
+    public static Func<T1, T3, TResult> Apply<T1, T2, T3, TResult>(this Func<T1, T2, T3, TResult> function, Unit arg1, T2 arg2, Unit arg3)
+        => (a1, a3) => function(a1, arg2, a3);
+
+    public static Func<T3, TResult> Apply<T1, T2, T3, TResult>(this Func<T1, T2, T3, TResult> function, T1 arg1, T2 arg2, Unit arg3)
+        => a3 => function(arg1, arg2, a3);
+
+    public static Func<T1, T2, TResult> Apply<T1, T2, T3, TResult>(this Func<T1, T2, T3, TResult> function, Unit arg1, Unit arg2, T3 arg3)
+        => (a1, a2) => function(a1, a2, arg3);
+
+    public static Func<T2, TResult> Apply<T1, T2, T3, TResult>(this Func<T1, T2, T3, TResult> function, T1 arg1, Unit arg2, T3 arg3)
+        => a2 => function(arg1, a2, arg3);
+
+    public static Func<T1, TResult> Apply<T1, T2, T3, TResult>(this Func<T1, T2, T3, TResult> function, Unit arg1, T2 arg2, T3 arg3)
+        => a1 => function(a1, arg2, arg3);
+}

Funcky/Functional/Discard.cs

@@ -0,0 +1,10 @@
+#pragma warning disable SA1300
+#pragma warning disable SA1649
+
+namespace Funcky;
+
+public class Discard
+{
+    public static readonly Unit _ = Unit.Value;
+    public static readonly Unit __ = Unit.Value;
+}

Funcky/PublicAPI.Unshipped.txt

@@ -1,9 +1,17 @@
 #nullable enable
+Funcky.Discard
+Funcky.Discard.Discard() -> void
 Funcky.RequireClass<T>
 Funcky.RequireClass<T>.RequireClass() -> void
 Funcky.RequireStruct<T>
 Funcky.RequireStruct<T>.RequireStruct() -> void
 static Funcky.Extensions.EnumerableExtensions.ElementAtOrNone<TSource>(this System.Collections.Generic.IEnumerable<TSource>! source, System.Index index) -> Funcky.Monads.Option<TSource>
+static Funcky.Extensions.FuncExtensions.Apply<T1, T2, T3, TResult>(this System.Func<T1, T2, T3, TResult>! function, Funcky.Unit arg1, Funcky.Unit arg2, T3 arg3) -> System.Func<T1, T2, TResult>!
+static Funcky.Extensions.FuncExtensions.Apply<T1, T2, T3, TResult>(this System.Func<T1, T2, T3, TResult>! function, Funcky.Unit arg1, T2 arg2, Funcky.Unit arg3) -> System.Func<T1, T3, TResult>!
+static Funcky.Extensions.FuncExtensions.Apply<T1, T2, T3, TResult>(this System.Func<T1, T2, T3, TResult>! function, Funcky.Unit arg1, T2 arg2, T3 arg3) -> System.Func<T1, TResult>!
+static Funcky.Extensions.FuncExtensions.Apply<T1, T2, T3, TResult>(this System.Func<T1, T2, T3, TResult>! function, T1 arg1, Funcky.Unit arg2, Funcky.Unit arg3) -> System.Func<T2, T3, TResult>!
+static Funcky.Extensions.FuncExtensions.Apply<T1, T2, T3, TResult>(this System.Func<T1, T2, T3, TResult>! function, T1 arg1, Funcky.Unit arg2, T3 arg3) -> System.Func<T2, TResult>!
+static Funcky.Extensions.FuncExtensions.Apply<T1, T2, T3, TResult>(this System.Func<T1, T2, T3, TResult>! function, T1 arg1, T2 arg2, Funcky.Unit arg3) -> System.Func<T3, TResult>!
 static Funcky.Extensions.ParseExtensions.ParseBigIntegerOrNone(this string? candidate, System.IFormatProvider? provider) -> Funcky.Monads.Option<System.Numerics.BigInteger>
 static Funcky.Extensions.ParseExtensions.ParseBigIntegerOrNone(this System.ReadOnlySpan<char> candidate, System.IFormatProvider? provider) -> Funcky.Monads.Option<System.Numerics.BigInteger>
 static Funcky.Extensions.ParseExtensions.ParseByteOrNone(this string? candidate, System.IFormatProvider? provider) -> Funcky.Monads.Option<byte>
@@ -43,3 +51,5 @@ static Funcky.Extensions.QueryableExtensions.ElementAtOrNone<TSource>(this Syste
 static Funcky.Extensions.StreamExtensions.ReadByteOrNone(this System.IO.Stream! stream) -> Funcky.Monads.Option<byte>
 static Funcky.Monads.OptionExtensions.ToNullable<TItem>(this Funcky.Monads.Option<TItem!> option, Funcky.RequireClass<TItem!>? ω = null) -> TItem?
 static Funcky.Monads.OptionExtensions.ToNullable<TItem>(this Funcky.Monads.Option<TItem> option, Funcky.RequireStruct<TItem>? ω = null) -> TItem?
+static readonly Funcky.Discard._ -> Funcky.Unit
+static readonly Funcky.Discard.__ -> Funcky.Unit