diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index bce6e6d7f4..72a067d18f 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -520,6 +520,7 @@ pub:
 	attrs           []Attr
 	ctdefine_idx    int = -1 // the index in fn.attrs of `[if xyz]`, when such attribute exists
 pub mut:
+	idx               int // index in an external container; can be used to refer to the function in a more efficient way, just by its integer index
 	params            []Param
 	stmts             []Stmt
 	defer_stmts       []DeferStmt
@@ -707,6 +708,7 @@ pub:
 	is_generated  bool // true for `[generated] module xyz` files; turn off notices
 	is_translated bool // true for `[translated] module xyz` files; turn off some checks
 pub mut:
+	idx              int    // index in an external container; can be used to refer to the file in a more efficient way, just by its integer index
 	path             string // absolute path of the source file - '/projects/v/file.v'
 	path_base        string // file name - 'file.v' (useful for tracing)
 	scope            &Scope
diff --git a/vlib/v/builder/interpreterbuilder/ibuilder.v b/vlib/v/builder/interpreterbuilder/ibuilder.v
index 06994d3ebe..452349d6cc 100644
--- a/vlib/v/builder/interpreterbuilder/ibuilder.v
+++ b/vlib/v/builder/interpreterbuilder/ibuilder.v
@@ -19,6 +19,6 @@ pub fn interpret_v(mut b builder.Builder) {
 
 	util.timing_start('INTERPRET')
 	mut e := eval.new_eval(b.table, b.pref)
-	e.eval(b.parsed_files)
+	e.eval(mut b.parsed_files)
 	util.timing_measure('INTERPRET')
 }
diff --git a/vlib/v/eval/eval.v b/vlib/v/eval/eval.v
index f932c50e9c..2e27e88268 100644
--- a/vlib/v/eval/eval.v
+++ b/vlib/v/eval/eval.v
@@ -30,28 +30,37 @@ pub mut:
 	return_values          []Object
 	cur_mod                string
 	cur_file               string
-	back_trace             []string
+	//
+	trace_file_paths     []string
+	trace_function_names []string
+	back_trace           []EvalTrace
 }
 
-pub fn (mut e Eval) eval(files []&ast.File) {
-	e.register_symbols(files)
+pub struct EvalTrace {
+	fn_idx   int
+	file_idx int
+	line     int
+}
+
+pub fn (mut e Eval) eval(mut files []&ast.File) {
+	e.register_symbols(mut files)
 	// println(files.map(it.path_base))
 	e.run_func(e.mods['main']['main'] or { ast.EmptyStmt{} } as ast.FnDecl)
 }
 
 // first arg is reciever (if method)
 pub fn (mut e Eval) run_func(func ast.FnDecl, _args ...Object) {
-	e.back_trace << func.name
+	e.back_trace << EvalTrace{func.idx, func.source_file.idx, func.pos.line_nr}
 	old_mod := e.cur_mod
-	e.cur_mod = func.mod
-
 	old_file := e.cur_file
+	e.cur_mod = func.mod
 	e.cur_file = func.file
 	defer {
 		e.cur_mod = old_mod
 		e.cur_file = old_file
 		e.back_trace.pop()
 	}
+	//
 	mut args := _args.clone()
 	if func.params.len != args.len && !func.is_variadic {
 		e.error('mismatched parameter length for $func.name: got `$args.len`, expected `$func.params.len`')
@@ -90,7 +99,7 @@ pub fn (mut e Eval) run_func(func ast.FnDecl, _args ...Object) {
 		}
 		if func.is_method {
 			print(e.back_trace)
-			println(func.receiver.typ - 65536)
+			println(func.receiver.typ.set_nr_muls(0))
 			e.local_vars[func.receiver.name] = Var{
 				val: args[0]
 				scope_idx: e.scope_idx
@@ -104,13 +113,19 @@ pub fn (mut e Eval) run_func(func ast.FnDecl, _args ...Object) {
 	}
 }
 
-pub fn (mut e Eval) register_symbols(files []&ast.File) {
-	for file in files {
+pub fn (mut e Eval) register_symbols(mut files []&ast.File) {
+	for mut file in files {
+		file.idx = e.trace_file_paths.len
+		e.trace_file_paths << file.path
 		// eprintln('registering file: $file.path_base')
 		mod := file.mod.name
-		e.register_symbol_stmts(file.stmts[1..], mod, file.path)
-
-		// eprintln('registered file: $file.path_base')
+		for mut stmt in file.stmts {
+			if mut stmt is ast.FnDecl {
+				stmt.idx = e.trace_function_names.len
+				e.trace_function_names << stmt.name
+			}
+		}
+		e.register_symbol_stmts(file.stmts, mod, file.path)
 	}
 	for mod, const_files in e.future_register_consts {
 		e.cur_mod = mod
@@ -133,14 +148,16 @@ pub fn (mut e Eval) register_symbols(files []&ast.File) {
 }
 
 pub fn (mut e Eval) register_symbol_stmts(stmts []ast.Stmt, mod string, file string) {
-	for stmt in stmts { // first is just module declaration, so ignore
+	for stmt in stmts {
 		e.register_symbol(stmt, mod, file)
 	}
 }
 
 pub fn (mut e Eval) register_symbol(stmt ast.Stmt, mod string, file string) {
 	match stmt {
-		ast.Module {}
+		ast.Module {
+			// ignore module declarations for now
+		}
 		ast.FnDecl {
 			// this mess because c error
 			x := ast.Stmt(stmt)
@@ -205,5 +222,10 @@ pub fn (mut e Eval) register_symbol(stmt ast.Stmt, mod string, file string) {
 }
 
 fn (e Eval) error(msg string) {
+	eprintln('> V interpeter backtrace:')
+	for idx, t in e.back_trace {
+		eprintln('  ${e.trace_file_paths[t.file_idx]}:${t.line + 1}:${e.trace_function_names[t.fn_idx]}')
+		// eprintln('${e.trace_file_paths[t.file_idx]}:${t.line + 1}:$t.fn_idx')
+	}
 	util.verror('interpreter', msg)
 }