Added the bra and ket commands for Dirac notation support (#134)

* Added the bra and ket commands for Dirac notation support

* Updated from comments in PR #134:
- Changed \bra and \ket to \Bra and \Ket
- Added a comment linking back to the original LaTeX package
- Added parse error unit tests for \Bra and \Ket

* Added render tests for \Bra and \Ket

* Added MathInline reference images for Bra and Ket

CSharpMath.CoreTests/LaTeXParserTest.cs

@@ -193,6 +193,32 @@ public void TestRadical() {
       Assert.Equal(@"\sqrt[3]{2}", LaTeXParser.MathListToLaTeX(list).ToString());
     }
 
+    [Fact]
+    public void TestBra() {
+      var list = ParseLaTeX(@"\Bra{i}");
+      Assert.Collection(list,
+        CheckAtom<Inner>("", inner => {
+          Assert.Equal("〈", inner.LeftBoundary.Nucleus);
+          Assert.Equal("|", inner.RightBoundary.Nucleus);
+          Assert.Collection(inner.InnerList, CheckAtom<Variable>("i"));
+        })
+      );
+      Assert.Equal(@"\Bra{i}", LaTeXParser.MathListToLaTeX(list).ToString());
+    }
+
+    [Fact]
+    public void TestKet() {
+      var list = ParseLaTeX(@"\Ket{i}");
+      Assert.Collection(list,
+        CheckAtom<Inner>("", inner => {
+          Assert.Equal("|", inner.LeftBoundary.Nucleus);
+          Assert.Equal("〉", inner.RightBoundary.Nucleus);
+          Assert.Collection(inner.InnerList, CheckAtom<Variable>("i"));
+        })
+      );
+      Assert.Equal(@"\Ket{i}", LaTeXParser.MathListToLaTeX(list).ToString());
+    }
+
     [
       Theory,
       InlineData(@"\left( 2 \right)", new[] { typeof(Inner) }, new[] { typeof(Number) }, @"(", @")", @"\left( 2\right) "),
@@ -1344,6 +1370,30 @@ public void TestHelpfulErrorMessage(string input, int index, string expected) {
       InlineData(@"\left(\begin{matrix}\right)", @"Error: Missing \end{matrix}
 ···(\begin{matrix}\right)
                        ↑ (pos 26)"),
+      InlineData(@"\Bra^2", @"Error: ^ cannot appear as an argument to a command
+\Bra^2
+    ↑ (pos 5)"),
+      InlineData(@"\Bra_2", @"Error: _ cannot appear as an argument to a command
+\Bra_2
+    ↑ (pos 5)"),
+      InlineData(@"\Bra&2", @"Error: & cannot appear as an argument to a command
+\Bra&2
+    ↑ (pos 5)"),
+      InlineData(@"\Bra}2", @"Error: } cannot appear as an argument to a command
+\Bra}2
+    ↑ (pos 5)"),
+      InlineData(@"\Ket^2", @"Error: ^ cannot appear as an argument to a command
+\Ket^2
+    ↑ (pos 5)"),
+      InlineData(@"\Ket_2", @"Error: _ cannot appear as an argument to a command
+\Ket_2
+    ↑ (pos 5)"),
+      InlineData(@"\Ket&2", @"Error: & cannot appear as an argument to a command
+\Ket&2
+    ↑ (pos 5)"),
+      InlineData(@"\Ket}2", @"Error: } cannot appear as an argument to a command
+\Ket}2
+    ↑ (pos 5)"),
     ]
     public void TestErrors(string badInput, string expected) {
       var (list, actual) = LaTeXParser.MathListFromLaTeX(badInput);

CSharpMath.Rendering.Tests/TestRenderingMathData.cs

@@ -99,5 +99,9 @@ public sealed class TestRenderingMathData : TestRenderingSharedData<TestRenderin
     public const string IntegralScripts = @"\int\int\int^{\infty}\int_0\int^{\infty}_0\int";
     public const string Logic = @"\neg(P\land Q) \iff (\neg P)\lor(\neg Q)";
     public const string LargerDelimiters = @"\left(\left[\left\{\left(\left[\left\{\left(\left[\left\{\left(\left[\left\{\square\right\}^\square\right]^\square\right)^\square\right\}^\square\right]^\square\right)^\square\right\}^\square\right]^\square\right)^\square\right\}^\square\right]^\square\right)^\square";
+    public const string BraSum = @"\frac{1}{\sqrt{2^n}} \sum_{i=0}^{2^n-1} \Bra{i}";
+    public const string KetSum = @"\frac{1}{\sqrt{2^n}} \sum_{i=0}^{2^n-1} \Ket{i}";
+    public const string LargeBra = @"\Bra{\frac{a}{2}+\frac{b}{3}}";
+    public const string LargeKet = @"\Ket{\frac{a}{2}+\frac{b}{3}}";
   }
 }

CSharpMath/Atom/LaTeXParser.cs

@@ -456,6 +456,16 @@ private string ReadCommand() {
           var operatorname = ReadString();
           if (!ExpectCharacter('}')) { SetError("Expected }"); return null; }
           return new LargeOperator(operatorname, null);
+        // Bra and Ket implementations are derived from Donald Arseneau's braket LaTeX package.
+        // See: https://www.ctan.org/pkg/braket
+        case "Bra":
+          var braContents = BuildInternal(true);
+          if (braContents is null) return null;
+          return new Inner(new Boundary("〈"), braContents, new Boundary("|"));
+        case "Ket":
+          var ketContents = BuildInternal(true);
+          if (ketContents is null) return null;
+          return new Inner(new Boundary("|"), ketContents, new Boundary("〉"));
         default:
           SetError("Invalid command \\" + command);
           return null;
@@ -862,6 +872,14 @@ private static void MathListToLaTeX
               builder.Append('{');
               MathListToLaTeX(inner.InnerList, builder, currentFontStyle);
               builder.Append('}');
+            } else if (inner.LeftBoundary.Nucleus == "〈" && inner.RightBoundary.Nucleus == "|") {
+              builder.Append(@"\Bra{");
+              MathListToLaTeX(inner.InnerList, builder, currentFontStyle);
+              builder.Append("}");
+            } else if (inner.LeftBoundary.Nucleus == "|" && inner.RightBoundary.Nucleus == "〉") {
+              builder.Append(@"\Ket{");
+              MathListToLaTeX(inner.InnerList, builder, currentFontStyle);
+              builder.Append("}");
             } else {
               static string BoundaryToLaTeX(Boundary delimiter) {
                 var command = LaTeXSettings.BoundaryDelimiters[delimiter];