Support for empty delimiters

src/WpfMath.Tests/ParserTests.fs

@@ -40,11 +40,28 @@ type ParserTests() =
         <| sprintf @"\left%sa\right%s" left right
         <| (formula <| fenced (openBrace lResult) (char 'a') (closeBrace rResult))
 
+    [<Theory>]
+    [<InlineData(".", ")", true, false)>]
+    [<InlineData("(", ".", false, true)>]
+    let ``Empty delimiters should work`` (left : string, right : string, isLeftEmpty : bool, isRightEmpty : bool) =
+        let empty = brace SymbolAtom.EmptyDelimiterName TexAtomType.Ordinary
+        let leftBrace = if isLeftEmpty then empty else (openBrace "lbrack")
+        let rightBrace = if isRightEmpty then empty else (closeBrace "rbrack")
+
+        assertParseResult
+        <| sprintf @"\left%sa\right%s" left right
+        <| (formula <| fenced leftBrace (char 'a') rightBrace)
+
     [<Fact>]
     let ``Unmatched delimiters should work`` () =
         assertParseResult
         <| @"\left)a\right|"
-        <| (formula <| fenced (closeBrace "rbrack") (char 'a') (SymbolAtom("vert", TexAtomType.Ordinary, true)))
+        <| (formula <| fenced (closeBrace "rbrack") (char 'a') (brace "vert" TexAtomType.Ordinary))
+
+    [<Fact>]
+    let ``Non-existing delimiter should throw exception`` () =
+        let markup = @"\left x\right)"
+        Assert.Throws<TexParseException>(fun () -> TexFormulaParser().Parse(markup) |> ignore)
 
     [<Fact>]
     let ``Expression in braces should be parsed`` () =

src/WpfMath.Tests/Utils.fs

@@ -8,7 +8,7 @@ let formula (root : Atom) : TexFormula =
 let char (c : char) : CharAtom = CharAtom(c)
 let styledChar (c : char, style:string) : CharAtom = CharAtom(c, style)
 let op (baseAtom : Atom) (useVertScripts : System.Nullable<bool>)  : BigOperatorAtom = BigOperatorAtom(baseAtom, null, null, useVertScripts)
-let opWithScripts (baseAtom : Atom) (subscript : Atom) (superscript : Atom) (useVertScripts : System.Nullable<bool>) 
+let opWithScripts (baseAtom : Atom) (subscript : Atom) (superscript : Atom) (useVertScripts : System.Nullable<bool>)
             : BigOperatorAtom = BigOperatorAtom(baseAtom, subscript, superscript, useVertScripts)
 let group (groupedAtom: Atom) : TypedAtom = TypedAtom(groupedAtom, TexAtomType.Ordinary, TexAtomType.Ordinary)
 let symbol (name : string) : SymbolAtom = SymbolAtom(name, TexAtomType.BinaryOperator, false)
@@ -19,5 +19,6 @@ let row (children : Atom seq) : RowAtom =
     result
 let fenced left body right : FencedAtom = FencedAtom(body, left, right)
 
-let openBrace (name : string) : SymbolAtom = SymbolAtom(name, TexAtomType.Opening, true)
-let closeBrace (name : string) : SymbolAtom = SymbolAtom(name, TexAtomType.Closing, true)
+let brace (name : string) (braceType : TexAtomType) : SymbolAtom = SymbolAtom(name, braceType, true)
+let openBrace (name : string) : SymbolAtom = brace name TexAtomType.Opening
+let closeBrace (name : string) : SymbolAtom = brace name TexAtomType.Closing

src/WpfMath/Data/TexFormulaSettings.xml

@@ -39,9 +39,10 @@
   <!-- character-to-delimiter-mappings
 
 These are used in the method "embrace(char,char)" from the class "Formula".
-The symbolnames must be defined in "TeXSymbols.xml" as delimiters (del="true")!! -->
+The symbolnames must be defined in "TexSymbols.xml" as delimiters (del="true")!! -->
 
   <CharacterToDelimiterMappings>
+    <Map char="." symbol="_emptyDelimiter"/>
     <Map char="(" symbol="lbrack"/>
     <Map char=")" symbol="rbrack"/>
     <Map char="[" symbol="lsqbrack"/>

src/WpfMath/Data/TexSymbols.xml

@@ -2,6 +2,9 @@
 
 <TeXSymbols>
 
+  <!-- special -->
+  <Symbol name="_emptyDelimiter" type="ord" del="true"/>
+
   <!-- miscellaneous symbols -->
 
   <Symbol name="%" type="ord"/>

src/WpfMath/FencedAtom.cs

@@ -1,7 +1,4 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 
 namespace WpfMath
 {
@@ -57,7 +54,7 @@ public override Box CreateBox(TexEnvironment environment)
             var minHeight = Math.Max((delta / 500) * delimeterFactor, 2 * delta - delimeterShortfall);
 
             // Create and add box for left delimeter.
-            if (LeftDelimeter != null)
+            if (LeftDelimeter != null && LeftDelimeter.Name != SymbolAtom.EmptyDelimiterName)
             {
                 var leftDelimeterBox = DelimiterFactory.CreateBox(this.LeftDelimeter.Name, minHeight, environment);
                 CentreBox(leftDelimeterBox, axis);
@@ -76,7 +73,7 @@ public override Box CreateBox(TexEnvironment environment)
                 resultBox.Add(Glue.CreateBox(this.BaseAtom.GetRightType(), TexAtomType.Closing, environment));
 
             // Create and add box for right delimeter.
-            if (this.RightDelimeter != null)
+            if (RightDelimeter != null && RightDelimeter.Name != SymbolAtom.EmptyDelimiterName)
             {
                 var rightDelimeterBox = DelimiterFactory.CreateBox(this.RightDelimeter.Name, minHeight, environment);
                 CentreBox(rightDelimeterBox, axis);

src/WpfMath/SymbolAtom.cs

@@ -1,14 +1,17 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 
 namespace WpfMath
 {
     // Atom representing symbol (non-alphanumeric character).
     internal class SymbolAtom : CharSymbol
     {
+        /// <summary>
+        /// Special name of empty delimiter symbol that shouldn't be rendered.
+        /// </summary>
+        internal const string EmptyDelimiterName = "_emptyDelimiter";
+
         // Dictionary of definitions of all symbols, keyed by name.
         private static IDictionary<string, SymbolAtom> symbols;
 
@@ -45,7 +48,7 @@ public static SymbolAtom GetAtom(string name)
 
         public static bool TryGetAtom(string name, out SymbolAtom atom)
         {
-            return symbols.TryGetValue(name, out atom);            
+            return symbols.TryGetValue(name, out atom);
         }
 
         public SymbolAtom(SymbolAtom symbolAtom, TexAtomType type)

src/WpfMath/TexFormulaParser.cs

@@ -120,6 +120,9 @@ internal static string GetDelimeterMapping(char character)
 
         internal static SymbolAtom GetDelimiterSymbol(string name)
         {
+            if (name == null)
+                return null;
+
             var result = SymbolAtom.GetAtom(name);
             if (!result.IsDelimeter)
                 return null;
@@ -154,7 +157,7 @@ private DelimiterInfo ParseUntilDelimiter(string value, ref int position, string
                 throw new TexParseException("Cannot find closing delimiter");
 
             var bodyRow = embeddedFormula.RootAtom as RowAtom;
-            var lastAtom = embeddedFormula.RootAtom as SymbolAtom ?? bodyRow.Elements.LastOrDefault();
+            var lastAtom = bodyRow?.Elements.LastOrDefault() ?? embeddedFormula.RootAtom;
             var lastDelimiter = lastAtom as SymbolAtom;
             if (lastDelimiter == null || !lastDelimiter.IsDelimeter)
                 throw new TexParseException($"Cannot find closing delimiter; got {lastDelimiter} instead");