diff --git a/exp/Exp.cs b/exp/Exp.cs
new file mode 100644
index 0000000..bb86539
--- /dev/null
+++ b/exp/Exp.cs
@@ -0,0 +1,99 @@
+using System.Collections.Immutable;
+using System.Runtime.CompilerServices;
+using imm;
+
+namespace exp;
+
+
+abstract public record class Exp<T> : imm.Versioned<Exp<T>>
+{
+	protected Exp()
+		:
+		base()
+	{
+
+	}
+
+	abstract public T exec();
+}
+
+public record class ConstantExp<T>( T value ) : Exp<T>
+{
+	public override T exec() => value;
+}
+
+public record class VarExp<T> : Exp<T>
+{
+
+	public T val = default!;
+
+	public VarExp()
+	{
+	}
+
+	public override T exec() => val;
+
+	public VarExp<T> set( T newVal )
+	{
+		return this with { val = newVal };
+	}
+}
+
+public ref struct RefHolder<T>
+{
+	public T val = default!;
+
+	public RefHolder()
+	{
+	}
+
+	public RefHolder( T initial )
+	{
+		val = initial;
+	}
+}
+
+
+/*
+
+public record class Op<T>( EntityId id, Func<Entity, T> fn,
+													[CallerMemberName] string dbgMethod = "",
+													[CallerFilePath] string dbgPath = "",
+													[CallerLineNumber] int dbgLine = 0,
+													[CallerArgumentExpression("fn")]
+													string dbgExp = ""
+) : Exp<T>
+{
+	public override T exec()
+	{
+		var ent = ent.Entity.Get( id );
+		if( ent == null )
+			throw new System.Exception( $"Op<{typeof(T).Name}>: Entity {id} not found" );
+
+		return fn( ent );
+	}
+}
+*/
+
+
+public record class StackExp<T>( VarExp<T> BaseVal ) : Exp<T>
+{
+	public VarExp<T> ModValue = BaseVal;
+
+	public ImmutableArray<Exp<T>> Adds = ImmutableArray<Exp<T>>.Empty;
+	public ImmutableArray<Exp<T>> Mults = ImmutableArray<Exp<T>>.Empty;
+
+	public override T exec()
+	{
+		return ModValue.exec();
+	}
+}
+
+
+
+
+
+
+/// //
+
+
diff --git a/logging/Log.cs b/logging/Log.cs
index 2077aa1..839a030 100644
--- a/logging/Log.cs
+++ b/logging/Log.cs
@@ -55,6 +55,7 @@ public struct SourceLoc
 	readonly string _reason = "";
 	readonly string _dbgName = "";
 	readonly string _dbgPath = "";
+	readonly string _dbgFile = "";
 	readonly int _dbgLine = -1;
 
 	public SourceLoc( string reason, string dbgName, string dbgPath, int dbgLine )
@@ -63,8 +64,12 @@ public struct SourceLoc
 		_dbgName = dbgName;
 		_dbgPath = dbgPath;
 		_dbgLine = dbgLine;
+
+		_dbgFile = log.whatFile( dbgPath );
 	}
 
+	public string ToLogString() => $"{_dbgFile}.{_dbgName}";
+
 	static public SourceLoc Record(
 																	string reason = "",
 																	[CallerMemberName] string dbgName = "",
@@ -285,8 +290,8 @@ static public class log
 	static ImmutableDictionary<int, string> s_files = ImmutableDictionary<int, string>.Empty;
 
 	#region Util
-	static public (string, string, int) record( [CallerMemberName] string dbgName = "", [CallerFilePath] string dbgPath = "", [CallerLineNumber] int dbgLine = -1 )
-		=> (dbgName, dbgPath, dbgLine);
+	static public SourceLoc loc( [CallerMemberName] string dbgName = "", [CallerFilePath] string dbgPath = "", [CallerLineNumber] int dbgLine = -1 )
+		=> new SourceLoc( "", dbgName, dbgPath, dbgLine );
 
 
 	static public string whatFile( string path )