(#272) Fix exception, improve exception reporting

src/WpfMath.Tests/ParserExceptionTests.fs

@@ -107,3 +107,8 @@ let ``Nonexistent color throws a TexParseException``(text: string): unit =
 let ``Invalid color numbers throw exceptions``(formula: string, colorModel: string): unit =
     let ex = assertParseThrows<TexParseException> formula
     Assert.Contains(colorModel, ex.Message)
+
+[<Fact>]
+let ``Invalid delimiter test``(): unit =
+    let ex = assertParseThrows<TexParseException> @"\left{2+2\right\}"
+    Assert.Contains(@"A delimiter should start from \, but got 2+2\right\", ex.Message)

src/WpfMath/Controls/FormulaControl.xaml.cs

@@ -199,6 +199,11 @@ private static object CoerceFormula(DependencyObject d, object baseValue)
                 control.SetError(e);
                 return "";
             }
+            catch (Exception e)
+            {
+                control.SetError(new TexParseException("Parser crash! " + e.Message, e));
+                return "";
+            }
         }
 
         private static object CoerceScaleValue(DependencyObject d, object baseValue)

src/XamlMath.Shared/TexFormulaParser.cs

@@ -401,7 +401,7 @@ private SymbolAtom ParseDelimiter(SourceSpan value, int start, ref int position)
             else
             {
                 if (delimiter[0] != escapeChar)
-                    throw new Exception($"Incorrect parser state: delimiter should start from {escapeChar}: {delimiter}");
+                    throw new TexParseException($"A delimiter should start from {escapeChar}, but got {delimiter}");
 
                 // Here goes the fancy business: for non-alphanumeric commands (e.g. \{, \\ etc.) we need to pass them
                 // through GetDelimeterMapping, but for alphanumeric ones, we don't.