A piecewise of Iverson brackets and provided integers compiles in LINQ

BREAKING-CHANGES.md

@@ -437,8 +437,9 @@ one where both sides are real, and `NaN` where either is not
 - A constant is taken over `Complex` where the expression is compiled over it. As a `long`, a constant widened only
   to `double`, so `sqrt(-1)`, `ln(-1)` and `arcsin(2)` were `NaN` and `1/0` was `+oo`
   ([#2235](https://github.com/asc-community/AngouriMath/issues/2235)).
-- An Iverson bracket, an `int?`, and a `provided` integer, a `long?`, are widened to `double` before a function takes
-  them. They threw `KeyNotFoundException` or `AngouriBugException`
+- A `provided` integer, a `long?`, and an Iverson bracket, an `int?`, are widened to `double` before a function or a
+  `piecewise` takes them. A `provided` integer threw `KeyNotFoundException` or `AngouriBugException` there, and an
+  Iverson bracket did not compile at all in 2.6.0
   ([#2237](https://github.com/asc-community/AngouriMath/issues/2237)).
 - `sgn(0)` is `0`, where `z / |z|` made it `NaN` ([#2238](https://github.com/asc-community/AngouriMath/issues/2238)).
 
@@ -447,6 +448,7 @@ one where both sides are real, and `NaN` where either is not
 | `"x + sqrt(-1)".ToEntity().Compile<Complex, Complex>("x")(0)` | `(NaN, 0)` | `(6.123233995736766E-17, 1)` |
 | `"x + 1/0".ToEntity().Compile<Complex, Complex>("x")(0)` | `(Infinity, 0)` | `(NaN, NaN)` |
 | `"x + sgn(-1 provided pi > 3)".ToEntity().Compile<Complex, Complex>("x")(1)` | throws `AngouriBugException` | `(0, 0)` |
+| `"piecewise(piecewise(-1 provided x > 0, 3) provided x > 0, x) + x".ToEntity().Compile<double, double>("x")(1)` | throws `KeyNotFoundException` | `0` |
 | `"sgn(x)".ToEntity().Compile<Complex, Complex>("x")(0)` | `(NaN, NaN)` | `(0, 0)` |
 
 ### A compiled product of real numbers is real at an infinity

Sources/.editorconfig

@@ -396,6 +396,9 @@ file_header_template=\nCopyright (c) 2019-2026 Angouri.\nAngouriMath is licensed
 [Tests/UnitTests/Common/LinqCompilationValueTest.cs]
 file_header_template=\nCopyright (c) 2019-2026 Angouri.\nAngouriMath is licensed under MIT.\nDetails: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.\nWebsite: https://am.angouri.org.\n
 
+[Tests/UnitTests/Common/PiecewiseOfNullableCompilationTest.cs]
+file_header_template=\nCopyright (c) 2019-2026 Angouri.\nAngouriMath is licensed under MIT.\nDetails: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.\nWebsite: https://am.angouri.org.\n
+
 [Tests/UnitTests/Common/CompileMatrixTest.cs]
 file_header_template=\nCopyright (c) 2019-2026 Angouri.\nAngouriMath is licensed under MIT.\nDetails: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.\nWebsite: https://am.angouri.org.\n
 

Sources/AngouriMath/Functions/Compilation/IntoLinq/CompilationProtocol.cs

@@ -386,6 +386,10 @@ private Expression HandlePiecewise(IEnumerable<Expression> en)
                     children[i] = ConvertType(children[i], typeof(bool?));
                     statements++;
                 }
+                // A case that is an Iverson bracket or a provided integer is widened to a double, as a function's
+                // operand is: MaxType has no int? or long?. https://github.com/asc-community/AngouriMath/issues/2237
+                else
+                    children[i] = NumericOperand(children[i]);
             if (statements > 0 && statements * 2 != children.Length)
                 throw new UncompilableNodeException("A piecewise whose cases are statements and numbers at once has no compiled form");
 

Sources/Tests/UnitTests/Common/PiecewiseOfNullableCompilationTest.cs

@@ -0,0 +1,40 @@
+//
+// Copyright (c) 2019-2026 Angouri.
+// AngouriMath is licensed under MIT.
+// Details: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.
+// Website: https://am.angouri.org.
+//
+
+using System.Numerics;
+using AngouriMath;
+using AngouriMath.Extensions;
+using Xunit;
+
+namespace AngouriMath.Tests.Common
+{
+    /// <summary>
+    /// A piecewise whose case is an Iverson bracket or a provided integer compiles in the LINQ compiler, where it threw
+    /// <c>KeyNotFoundException</c>: its case types, an <c>int?</c> and a <c>long?</c>, were not in the widening table.
+    /// <a href="https://github.com/asc-community/AngouriMath/issues/2237">#2237</a>
+    /// </summary>
+    [Trait("Area", "Common")]
+    public sealed class PiecewiseOfNullableCompilationTest
+    {
+        [Theory]
+        [InlineData("sin(piecewise(iverson(x > 0) provided x > 0, sin(2)))", 2)]
+        [InlineData("sin(piecewise(iverson(x > 0) provided x > 0, sin(2)))", -2)]
+        [InlineData("exp(piecewise(2^x provided x > 0, iverson(x > 0)))", -1)]
+        [InlineData("abs(piecewise((-1)^2 provided x > 0, iverson(-1 > 0)))", 1)]
+        [InlineData("piecewise(iverson(sinh(3) > 0) provided x > 0, tan(-1))", 1)]
+        [InlineData("piecewise(piecewise(-1 provided x > 0, 3) provided x > 0, x) + x", 1)]
+        [InlineData("piecewise(piecewise(-1 provided x > 0, 3) provided x > 0, x) + x", -1)]
+        public void ItIsWhatEvaluationGives(string expression, double at)
+        {
+            var expected = ((Entity.Number.Complex)expression.ToEntity().Substitute("x", at).Evaled).ToNumerics();
+            var linq = expression.ToEntity().Compile<Complex, Complex>("x")(at);
+            var real = expression.ToEntity().Compile<double, double>("x")(at);
+            Assert.True(Complex.Abs(expected - linq) < 1e-12, $"{expression} at {at}: {expected} evaluated, {linq} by LINQ");
+            Assert.True(System.Math.Abs(expected.Real - real) < 1e-12, $"{expression} at {at}: {expected} evaluated, {real} over double");
+        }
+    }
+}