Add Macro > Arguments > Instance argument

assets/InstanceExprArgMacro.hx

@@ -0,0 +1,30 @@
+import haxe.macro.Expr;
+import haxe.macro.ExprTools;
+import haxe.macro.MacroStringTools;
+
+// use this for macros or other classes
+class Logger {
+	public final id:String;
+	public function new(id:String) {
+		this.id = id;
+	}
+
+	inline public function log(data:Any, logID:String, ?pos) {
+		haxe.Log.trace('$id: $logID = [$data]', pos);
+	}
+
+	macro public function logExpr(instance:Expr, data:Expr):Expr {
+		return eval(instance, data);
+	}
+
+	#if macro
+	static public function eval(instance:Expr, obj:Expr):Expr {
+		final id = MacroStringTools.formatString('${ExprTools.toString(obj)}', obj.pos);
+
+		return macro {
+			@:pos(obj.pos)
+			$instance.log($obj, $id);
+		};
+	}
+	#end
+}

assets/InstanceExprArgUsage.hx

@@ -0,0 +1,12 @@
+class Test {
+	static function main() {
+		final factLogger = new Logger("Fact");
+		final lieLogger = new Logger("Lie");
+
+		final theory1 = {statement: "Haxe is great!", conclusion: true};
+		final theory2 = {statement: "7 > 9", conclusion: false};
+
+		(theory1.conclusion ? factLogger : lieLogger).logExpr(theory1.statement);
+		(theory2.conclusion ? factLogger : lieLogger).logExpr(theory2.statement);
+	}
+}

content/09-macro.md

@@ -90,6 +90,23 @@ If the final argument of a macro is of type `Array<Expr>`, the macro accepts an
 
 
 
+<!--label:macro-instance-arg-->
+#### Instance Argument
+
+If the macro is an instance method, the first arg will be the expression used to reference the instance:
+
+[code asset](assets/InstanceExprArgMacro.hx)
+
+Usage:
+
+[code asset](assets/InstanceExprArgUsage.hx)
+
+This outputs at runtime:
+```
+Test.hx:9: Fact: theory1.statement = [Haxe is great!]
+Test.hx:10: Lie: theory2.statement = [7 > 9]
+```
+
 
 
 <!--label:macro-reification-->