Parser/XnParser.cs

@@ -199,11 +199,13 @@ namespace XNeedle.Parser
             from ws1 in Parse.WhiteSpace.Many().Optional()
             from open in Parse.Char('{')
             from ws2 in Parse.WhiteSpace.Many().Optional()
-            from expressions in Parse.Ref(() => BangObject)
+            from expressions in (
-                .Or(Parse.Ref(() => RuleObject))
+                from expr in Parse.Ref(() => BangObject)
-                .Or(ExprPart(ctx).Select(e => (Part)e))
+                    .Or(Parse.Ref(() => RuleObject))
-                .DelimitedBy(Parse.Char(';').Token())
+                    .Or(ExprPart(ctx).Select(e => (Part)e))
-            from tailingsemi in Parse.Char(';').Optional()
+                from semi in Parse.Char(';').Token()
+                select expr
+            ).Many()
             from ws3 in Parse.WhiteSpace.Many().Optional()
             from close in Parse.Char('}')
             select new Bang{Name = new string([.. name]), Arguments = arguments, Body = expressions};
@@ -214,15 +216,23 @@ namespace XNeedle.Parser
             from ws1 in Parse.WhiteSpace.Many().Optional()
             from open in Parse.Char('{')
             from ws2 in Parse.WhiteSpace.Many().Optional()
-            from expressions in Parse.Ref(() => BangObject)
+            from expressions in (
-                .Or(Parse.Ref(() => RuleObject))
+                from expr in Parse.Ref(() => BangObject)
-                .Or(ExprPart(ctx).Select(e => (Part)e))
+                    .Or(Parse.Ref(() => RuleObject))
-                .DelimitedBy(Parse.Char(';').Token())
+                    .Or(ExprPart(ctx).Select(e => (Part)e))
-            from tailingsemi in Parse.Char(';').Optional()
+                from semi in Parse.Char(';').Token()
+                select expr
+            ).Many()
             from ws3 in Parse.WhiteSpace.Many().Optional()
             from close in Parse.Char('}')
             select new Rule{XPathSelector = selector, Body = expressions};
-    
+
+        public static readonly Parser<IEnumerable<Part>> Rules =
+            (from rule in RuleObject.Token()
+             from semi in Parse.Char(';').Token()
+             select rule)
+            .Many()
+            .End();
 
         static public string StripComments(string source)
         {

Program.cs

@@ -40,10 +40,10 @@ namespace XNeedle
 
             var rawSource = File.ReadAllText(opts.XnDefinition);
             var xnSource = XnParser.StripComments(rawSource);
-            Rule masterRule;
+            IEnumerable<Part> rules;
             try
             {
-                masterRule = (Rule)XnParser.RuleObject.Parse(xnSource);
+                rules = XnParser.Rules.Parse(xnSource);
             }
             catch (ParseException ex)
             {
@@ -54,11 +54,19 @@ namespace XNeedle
 
                 if (showPosition)
                 {
-                    Console.Error.WriteLine($"{opts.XnDefinition}({line},{col}): parse error: {ex.Message}");
+                    var msg = ex.Message;
+                    var hint = (msg.Contains("expected }") && !msg.Contains("expected ';'"))
+                        ? "Hint: a missing ';' terminator may be located just after this position"
+                        : "";
+                    Console.Error.WriteLine($"{opts.XnDefinition}({line},{col}): parse error: {msg}");
                     var srcLine = line <= lines.Length ? lines[line - 1].TrimEnd() : "";
                     var pointer = new string(' ', Math.Max(0, col - 1)) + "^";
                     Console.Error.WriteLine($"  {srcLine}");
                     Console.Error.WriteLine($"  {pointer}");
+                    if (!string.IsNullOrEmpty(hint))
+                    {
+                        Console.Error.WriteLine($"\n{hint}");
+                    }
                 }
                 else
                 {
@@ -69,7 +77,16 @@ namespace XNeedle
             var doc = XDocument.Load(opts.Input, LoadOptions.PreserveWhitespace);
             var encoding = XmlRoundtripWriter.DetectEncoding(File.ReadAllBytes(opts.Input));
             var sloc = new SourceLocation(opts.Input, encoding);
-            masterRule.Transform(doc, sloc);
+            try
+            {
+                foreach (var rule in rules.OfType<Rule>())
+                    rule.Transform(doc, sloc);
+            }
+            catch (RequireException ex)
+            {
+                Console.Error.WriteLine($"{ex.SLoc.FilePath}({ex.SLoc.LineNumber}): require error: {ex.UserMessage}");
+                return;
+            }
             using var writer = XmlRoundtripWriter.Create(opts.Input, opts.Output);
             doc.WriteTo(writer);
             Console.WriteLine($"Applied \"{opts.XnDefinition}\" to \"{opts.Input}\" and saved result to \"{opts.Output}\"");

Transformation/ContextFunctions.cs

@@ -187,5 +187,18 @@ namespace XNeedle.Transformation
             }
             return "";
         }
+
+        public static string require(Context ctx, string message = "Required node not present")
+        {
+            if (ctx.Node == null)
+            {
+                throw new RequireException{SLoc=ctx.SLoc, UserMessage=message};
+            }
+            else
+            {
+                Console.WriteLine(ctx.Node.ToString());
+            }
+            return "";
+        }
     }
 }

Transformation/RequireException.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+using System.Xml;
+using System.Xml.Linq;
+using System.Xml.XPath;
+using XNeedle;
+using XNeedle.Parser.Elements;
+
+namespace XNeedle.Transformation
+{
+    public class RequireException : Exception
+    {
+        public SourceLocation SLoc { get; set; }
+        public required string UserMessage { get; set; }  
+    }
+}

Transformation/Rule.cs

@@ -22,15 +22,19 @@ namespace XNeedle.Transformation
 
         public override void Operate(Context ctx)
         {
-            if(ctx.Node is null)
+            var nodes = ctx.Node?.XPathSelectElements(XPathSelector);
-            {
+            if(nodes is null || nodes.Count() == 0)
-                return;
-            }
-            var nodes = ctx.Node.XPathSelectElements(XPathSelector);
-            if(nodes is null)
             {
+                var nullCtx = ctx.Clone();
+                nullCtx.Node = null;
+                nullCtx.SLoc = ctx.SLoc.WithLineNumber(-1);
+                foreach (var b in Body)
+                {
+                    b.Operate(nullCtx);
+                }
                 return;
             }
+  
             foreach (XElement n in nodes)
             {
                 var loopCtx = ctx.Clone();