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I'm making a little DFA compiler that renders directly to an assembly using System.Reflection.Emit

Note that below there's an FALIB define. This will always be defined when the compiler is used.

My IL code is supposed to implement a concrete version of this

#if FALIB
public
#endif
abstract partial class FARunner
{
		
	protected abstract int MatchImpl(LexContext lc);
	protected abstract FAMatch SearchImpl(LexContext lc);
	/// <summary>
	/// Searches through text for the next occurance of a pattern matchable by this machine
	/// </summary>
	/// <param name="lc">The <see cref="LexContext"/> with the text to search</param>
	/// <returns>A series of <see cref="FAMatch"/> instances with the matches</returns>
	public IEnumerable<FAMatch> Search(LexContext lc)
	{
		while(lc.Current!=LexContext.EndOfInput)
		{
			yield return SearchImpl(lc);
		}
	}
	/// <summary>
	/// Indicates whether this machine will match the indicated text
	/// </summary>
	/// <param name="lc">A <see cref="LexContext"/> containing the text</param>
	/// <returns>The accept symbol if matched, otherwise -1.</returns>
	public int Match(LexContext lc)
	{
		return MatchImpl(lc);
	}
	/// <summary>
	/// Searches through text for the next occurance of a pattern matchable by this machine
	/// </summary>
	/// <param name="@string">The <see cref="IEnumerable{char}"/> with the text to search</param>
	/// <returns>A series of <see cref="FAMatch"/> instances with the matches</returns>
	public IEnumerable<FAMatch> Search(IEnumerable<char> @string)
	{
		foreach (var match in Search(LexContext.Create(@string)))
		{
			yield return match;
		}
	}
	/// <summary>
	/// Searches through text for the next occurance of a pattern matchable by this machine
	/// </summary>
	/// <param name="reader">The <see cref="TextReader"/> with the text to search</param>
	/// <returns>A series of <see cref="FAMatch"/> instances with the matches</returns>
	public IEnumerable<FAMatch> Search(TextReader reader)
	{
		foreach (var match in Search(LexContext.CreateFrom(reader)))
		{
			yield return match;
		}
	}
	/// <summary>
	/// Indicates whether this machine will match the indicated text
	/// </summary>
	/// <param name="text">The text</param>
	/// <returns>True if the passed in text was a match, otherwise false.</returns>
	public int Match(IEnumerable<char> text)
	{
		return Match(LexContext.Create(text));
	}

}


It just needs to fill in SearchImpl and MatchImpl with concrete methods, which I've done although they currently throw not-implemented.

The trouble I'm having is this - the MatchImpl method calls just fine.

The SearchImpl method - well it's weird. It not only doesn't get called, neither do any of the methods that delegate to it. I don't get an error, compiler thrown or runtime. It just silently fails when I try to call it.

The only thing I can think of is something about my return type being a struct. That's the only difference here that I can see - well that and the name.

What I have tried:

C#
public static partial class FACompiler
{
	public static FARunner Compile(this FA fa, IProgress<int> progress = null)
	{
		if (fa == null) throw new ArgumentNullException(nameof(fa));
		fa = fa.ToDfa(progress);
		var name = "FARunner" + fa.GetHashCode();
		var asmName = new AssemblyName(name);
		var asm = Thread.GetDomain().DefineDynamicAssembly(asmName, AssemblyBuilderAccess.Run);
		ModuleBuilder mod = asm.DefineDynamicModule("M"+name);
		TypeBuilder type = mod.DefineType(name, TypeAttributes.Public | TypeAttributes.Sealed, typeof(FARunner));
		Type[] paramTypes = new Type[] { typeof(LexContext) };
		Type searchReturnType = typeof(FAMatch);
		MethodBuilder searchImpl = type.DefineMethod("SearchImpl", MethodAttributes.Public | MethodAttributes.ReuseSlot |
			MethodAttributes.Virtual | MethodAttributes.HideBySig, searchReturnType, paramTypes);
		ILGenerator searchGen = searchImpl.GetILGenerator();
		searchGen.ThrowException(typeof(NotImplementedException));
			
		MethodInfo searchImplBase = typeof(FARunner).GetMethod("SearchImpl",BindingFlags.NonPublic | BindingFlags.Instance);
		type.DefineMethodOverride(searchImpl, searchImplBase);

		Type matchReturnType = typeof(int);
		MethodBuilder match = type.DefineMethod("MatchImpl", MethodAttributes.Public | MethodAttributes.ReuseSlot |
			MethodAttributes.Virtual | MethodAttributes.HideBySig, matchReturnType, paramTypes);
		ILGenerator matchGen = match.GetILGenerator();
		matchGen.ThrowException(typeof(NotImplementedException));
		MethodInfo matchBase = typeof(FARunner).GetMethod("MatchImpl", BindingFlags.NonPublic | BindingFlags.Instance);
		type.DefineMethodOverride(match, matchBase);

		Type newType = type.CreateType();

		return (FARunner)Activator.CreateInstance(newType);

	}
}


I also tried adding these lines to adjust the stack in case I needed it filled even in the event of a throw:

C#
LocalBuilder famatch = searchGen.DeclareLocal(typeof(FAMatch));
searchGen.Emit(OpCodes.Ldloca_S, famatch);
searchGen.Emit(OpCodes.Initobj, typeof(FAMatch));


I get the same results.
Posted
Updated 5-Jan-24 4:53am
v3
Comments
0x01AA 5-Jan-24 11:22am    
And if you run it in debugger with all exceptions active (i mean debugger stops on _every_ exception) you get also no exceptions?
This, because I think to remember some very strange behaviour, where deep in .NET some exceptions will be 'catch(...){}'
honey the codewitch 5-Jan-24 11:41am    
Thanks for the suggestion. I just tried that. I get nothing. In fact, it runs the code after that line, so I don't think it's throwing anything.
0x01AA 5-Jan-24 12:10pm    
You are very welcome.
Btw. can one debug through the IL code? I know that from c++ (Embarcadero) where I can debug the assembled code instead of c++ source. Only a thought from a noob ;)
honey the codewitch 5-Jan-24 12:53pm    
There's probably a way but I don't know it.

1 solution

I don't understand why, but when I took yields out of my FARunner class and hand implemented my enumerator instead everything worked fine.

I'm closing this as solved even though I'm mystified.
 
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