Parse inline math spans inside text commands

CSharpMath.Core.Tests/Atom/LaTeXParserTest.cs

@@ -1156,6 +1156,71 @@ public void TestText() {
       Assert.Equal(@"\mathrm{\pounds x\  y}", LaTeXParser.MathListToLaTeX(list).ToString());
     }
 
+    [Fact]
+    public void TestInlineMathInsideText() {
+      var list = ParseLaTeX(@"\text{before $x+1$ after}");
+      Assert.Equal(FontStyle.Roman, list[0].FontStyle);
+      Assert.Equal(FontStyle.Default, list[7].FontStyle);
+      Assert.Equal(FontStyle.Default, list[8].FontStyle);
+      Assert.Equal(FontStyle.Default, list[9].FontStyle);
+      Assert.Equal(FontStyle.Roman, list[10].FontStyle);
+      Assert.Equal(@"\mathrm{before\  }x+1\mathrm{\  after}", LaTeXParser.MathListToLaTeX(list).ToString());
+    }
+
+    [Fact]
+    public void TestEscapedDollarInsideTextIsLiteralAndRoundTrips() {
+      var list = ParseLaTeX(@"\text{price \$5}");
+      Assert.Contains(list, atom => atom is Ordinary { Nucleus: "$" });
+      var serialized = LaTeXParser.MathListToLaTeX(list).ToString();
+      Assert.Contains(@"\$", serialized);
+      Assert.Equal(list, ParseLaTeX(serialized));
+    }
+
+    [Fact]
+    public void TestTextInlineMathCommandsBracesScriptsAndEscapedDollarRoundTrip() {
+      var input = @"\text{cases: $\frac{n^{2}}{2}$, \mathbf{Roman} and \$ literal}";
+      var list = ParseLaTeX(input);
+      var serialized = LaTeXParser.MathListToLaTeX(list).ToString();
+      Assert.Equal(list, ParseLaTeX(serialized));
+    }
+
+    [Fact]
+    public void TestIssue205CasesRoundTrip() {
+      var input = @"f(n) = \begin{cases} n/2, & \text{if $n$ is even} \\ 3n+1, & \text{if $n$ is odd} \end{cases}";
+      var list = ParseLaTeX(input);
+      Assert.Equal(list, ParseLaTeX(LaTeXParser.MathListToLaTeX(list).ToString()));
+    }
+
+    [Fact]
+    public void TestUnbalancedInlineMathInsideTextReportsSourcePosition() {
+      var input = @"\text{before $x after}";
+      var builder = new LaTeXParser(input);
+      var (list, error) = builder.Build();
+      Assert.Null(list);
+      Assert.Contains("Expected character not found: $", error);
+      Assert.Equal(input.Length - 1, builder.NextChar);
+      Assert.EndsWith($"↑ (pos {input.Length - 1})", LaTeXParser.HelpfulErrorMessage(error!, input, builder.NextChar));
+    }
+
+    [Fact]
+    public void TestTextStateIsRestoredWhenTextArgumentFails() {
+      var builder = new LaTeXParser(@"\text{bad \notacommand}");
+      var (_, error) = builder.Build();
+      Assert.NotNull(error);
+      Assert.False(builder.TextMode);
+      Assert.Equal(FontStyle.Default, builder.CurrentFontStyle);
+    }
+
+    [Theory]
+    [InlineData(@"\text{a $$ b}")]
+    [InlineData(@"\text{a $$$ b}")]
+    public void TestDisplayDollarDelimitersInsideTextAreRejected(string input) {
+      var builder = new LaTeXParser(input);
+      var (_, error) = builder.Build();
+      Assert.Contains("Display math delimiters $$ are not allowed inside text", error);
+      Assert.Equal(input.IndexOf("$$", StringComparison.Ordinal) + 1, builder.NextChar);
+    }
+
     [Fact]
     public void TestScriptOrdering() {
       var list = ParseLaTeX(@"\int_a^b");
@@ -1634,4 +1699,4 @@ public void TestErrorSurrogates() {
       }
     }
   }
-}
+}

CSharpMath.Rendering.Tests/TestRenderingMathData.cs

@@ -15,6 +15,7 @@ public sealed class TestRenderingMathData : TestRenderingSharedData<TestRenderin
     public const string BraSum = @"\frac{1}{\sqrt{2^n}} \sum_{i=0}^{2^n-1} \Bra{i}";
 
     public const string Cases = @" w \equiv \begin{cases} 0 & \text{for}\ c = d = 0\\ \sqrt{|c|}\,\sqrt{\frac{1+\sqrt{1+(d/c)^2}}{2}} &\text{for}\ |c| \geq |d|\\ \sqrt{|d|}\,\sqrt{\frac{|c/d| + \sqrt{1+(c/d)^2}}{2}} &\text{for}\ |c|<|d| \end{cases}";
+    public const string Issue205NestedTextMath = @"f(n) = \begin{cases} n/2, & \text{if $n$ is even} \\ 3n+1, & \text{if $n$ is odd} \end{cases}";
     public const string Choose = @"{6 \choose x}";
     public const string Commands = @"5\times(-2 \div 1) = -10";
 
@@ -135,4 +136,4 @@ public sealed class TestRenderingMathData : TestRenderingSharedData<TestRenderin
 
     public const string VectorProjection = @"Proj_\vec{v}\vec{u}=|\vec u|\cos\theta\times\frac\vec v{|\vec v|}=|\vec u|\frac{\vec u \cdot \vec v}{|\vec u||\vec v|}\times\frac\vec v{|\vec v|}\\\text{Suppose \mathit{u} and \mathit v are unit vectors, }Proj_\vec v\vec u = (\vec u\cdot\vec v)\vec v";
   }
-}
+}

CSharpMath/Atom/LaTeXParser.cs

@@ -60,6 +60,28 @@ private Result<MathList> BuildInternal(bool oneCharOnly, char stopChar = '\0', M
       r ??= new MathList();
       MathAtom? prevAtom = null;
       while (HasCharacters) {
+        if (TextMode && Chars[NextChar] == '$') {
+          NextChar++;
+          if (HasCharacters && Chars[NextChar] == '$')
+            return "Display math delimiters $$ are not allowed inside text";
+          var oldTextMode = TextMode;
+          var oldFontStyle = CurrentFontStyle;
+          TextMode = false;
+          CurrentFontStyle = FontStyle.Default;
+          Result<MathList> inlineMath;
+          try {
+            inlineMath = BuildInternal(false, '$');
+          } finally {
+            TextMode = oldTextMode;
+            CurrentFontStyle = oldFontStyle;
+          }
+          if (inlineMath.Error is string inlineError) return inlineError;
+          r.Append(inlineMath.Match(value => value, _ => throw new InvalidCodePathException("Inline math unexpectedly failed")));
+          prevAtom = r.Atoms.LastOrDefault();
+          continue;
+        }
+        if (stopChar == '$' && Chars[NextChar] == '}')
+          return "Expected character not found: $";
         MathAtom? atom = null;
         if (Chars[NextChar] == stopChar && stopChar > '\0') {
           NextChar++;
@@ -702,6 +724,9 @@ static bool MathAtomToLaTeX(MathAtom atom, StringBuilder builder,
           case { Nucleus: "\u2212" }:
             builder.Append('-');
             break;
+          case { Nucleus: "$" }:
+            builder.Append(@"\$");
+            break;
           case { Nucleus: var aNucleus }:
             builder.Append(aNucleus);
             break;
@@ -731,4 +756,4 @@ public static StringBuilder MathListToLaTeX(MathList mathList, StringBuilder? sb
       return sb;
     }
   }
-}
+}

CSharpMath/Atom/LaTeXSettings.cs

@@ -364,9 +364,14 @@ public static class LaTeXSettings {
           var readsToEnd =
             !command.AsSpan().StartsWithInvariant("math")
             && !command.AsSpan().StartsWithInvariant("text");
-          return (readsToEnd ? parser.ReadUntil(stopChar, accumulate) : parser.ReadArgument()).Bind(r => {
+          Result<MathList> result;
+          try {
+            result = readsToEnd ? parser.ReadUntil(stopChar, accumulate) : parser.ReadArgument();
+          } finally {
             parser.CurrentFontStyle = oldFontStyle;
             parser.TextMode = oldSpacesAllowed;
+          }
+          return result.Bind(r => {
             if (readsToEnd)
               return OkStop(accumulate);
             else return OkStyled(r);
@@ -1189,4 +1194,4 @@ atom is Accent accent
         // \varsupsetneqq -> ⫌ + U+FE00 (Variation Selector 1) Not dealing with variation selectors, thank you very much
       };
   }
-}
+}