diff --git a/vlib/v/ast/str.v b/vlib/v/ast/str.v
index 7d54455b8a..2e2510dbea 100644
--- a/vlib/v/ast/str.v
+++ b/vlib/v/ast/str.v
@@ -17,6 +17,22 @@ pub fn (node &FnDecl) modname() string {
 	return pamod
 }
 
+// fkey returns a unique name of the function/method.
+// it is used in table.used_fns and v.markused.
+pub fn (node &FnDecl) fkey() string {
+	if node.is_method {
+		return '${int(node.receiver.typ)}.$node.name'
+	}
+	return node.name
+}
+
+pub fn (node &CallExpr) fkey() string {
+	if node.is_method {
+		return '${int(node.receiver_type)}.$node.name'
+	}
+	return node.name
+}
+
 // These methods are used only by vfmt, vdoc, and for debugging.
 pub fn (node &FnDecl) stringify(t &Table, cur_mod string, m2a map[string]string) string {
 	mut f := strings.new_builder(30)
diff --git a/vlib/v/builder/builder.v b/vlib/v/builder/builder.v
index a9379732d0..f3b2c77b0a 100644
--- a/vlib/v/builder/builder.v
+++ b/vlib/v/builder/builder.v
@@ -10,6 +10,7 @@ import v.checker
 import v.parser
 import v.depgraph
 import v.markused
+import v.callgraph
 
 pub struct Builder {
 pub:
@@ -86,6 +87,9 @@ pub fn (mut b Builder) middle_stages() ? {
 	if b.pref.skip_unused {
 		markused.mark_used(mut b.table, b.pref, b.parsed_files)
 	}
+	if b.pref.show_callgraph {
+		callgraph.show(mut b.table, b.pref, b.parsed_files)
+	}
 }
 
 pub fn (mut b Builder) front_and_middle_stages(v_files []string) ? {
diff --git a/vlib/v/callgraph/callgraph.v b/vlib/v/callgraph/callgraph.v
new file mode 100644
index 0000000000..e5c2b4b691
--- /dev/null
+++ b/vlib/v/callgraph/callgraph.v
@@ -0,0 +1,146 @@
+module callgraph
+
+import v.ast
+import v.ast.walker
+import v.pref
+import strings
+
+// callgraph.show walks the AST, starting at main() and prints a DOT output describing the calls
+// that function make transitively
+pub fn show(mut table ast.Table, pref &pref.Preferences, ast_files []&ast.File) {
+	mut mapper := &Mapper{
+		pref: pref
+		table: table
+	}
+	mapper.sb.writeln('digraph G {')
+	mapper.sb.writeln('\tedge [fontname="Helvetica",fontsize="10",labelfontname="Helvetica",labelfontsize="10",style="solid",color="black"];')
+	mapper.sb.writeln('\tnode [fontname="Helvetica",fontsize="10",style="filled",fontcolor="black",fillcolor="white",color="black",shape="box"];')
+	mapper.sb.writeln('\trankdir="LR";')
+	// Node14 [shape="box",label="PrivateBase",URL="$classPrivateBase.html"];
+	// Node15 -> Node9 [dir=back,color="midnightblue",fontsize=10,style="solid"];
+	for afile in ast_files {
+		walker.walk(mapper, afile)
+	}
+	mapper.sb.writeln('}')
+	println(mapper.sb.str())
+}
+
+[heap]
+struct Mapper {
+	pos int
+mut:
+	pref            &pref.Preferences
+	table           &ast.Table
+	file            &ast.File   = 0
+	node            &ast.Node   = 0
+	fn_decl         &ast.FnDecl = 0
+	caller_name     string
+	dot_caller_name string
+	is_caller_used  bool
+	sb              strings.Builder = strings.new_builder(1024)
+}
+
+fn (mut m Mapper) dot_normalise_node_name(name string) string {
+	res := name.replace_each([
+		'.',
+		'_',
+		'==',
+		'op_eq',
+		'>=',
+		'op_greater_eq',
+		'<=',
+		'op_lesser_eq',
+		'>',
+		'op_greater',
+		'<',
+		'op_lesser',
+		'+',
+		'op_plus',
+		'-',
+		'op_minus',
+		'/',
+		'op_divide',
+		'*',
+		'op_multiply',
+		'^',
+		'op_xor',
+		'|',
+		'op_or',
+		'&',
+		'op_and',
+	])
+	return res
+}
+
+fn (mut m Mapper) fn_name(fname string, receiver_type ast.Type, is_method bool) string {
+	if !is_method {
+		return fname
+	}
+	rec_sym := m.table.get_type_symbol(receiver_type)
+	return '${rec_sym.name}.$fname'
+}
+
+fn (mut m Mapper) dot_fn_name(fname string, recv_type ast.Type, is_method bool) string {
+	if is_method {
+		return 'Node_method_' + int(recv_type).str() + '_' + m.dot_normalise_node_name(fname)
+	}
+	return 'Node_fn_' + m.dot_normalise_node_name(fname)
+}
+
+fn (mut m Mapper) visit(node &ast.Node) ? {
+	m.node = unsafe { node }
+	match node {
+		ast.File {
+			m.file = unsafe { &node }
+		}
+		ast.Stmt {
+			match node {
+				ast.FnDecl {
+					m.is_caller_used = true
+					if m.pref.skip_unused {
+						m.is_caller_used = m.table.used_fns[node.fkey()]
+					}
+					m.fn_decl = unsafe { &node }
+					m.caller_name = m.fn_name(node.name, node.receiver.typ, node.is_method)
+					m.dot_caller_name = m.dot_fn_name(node.name, node.receiver.typ, node.is_method)
+					if m.is_caller_used {
+						if m.caller_name == 'main.main' {
+							m.sb.writeln('\t$m.dot_caller_name [label="fn main()",color="blue",height=0.2,width=0.4,fillcolor="#00FF00",tooltip="The main program entry point.",shape=oval];')
+						} else {
+							m.sb.writeln('\t$m.dot_caller_name [shape="box",label="$m.caller_name"];')
+						}
+					}
+				}
+				else {}
+			}
+		}
+		ast.Expr {
+			match node {
+				ast.CallExpr {
+					if m.is_caller_used {
+						dot_called_name := m.dot_fn_name(node.name, node.receiver_type,
+							node.is_method)
+						// Node15 -> Node9 [dir=back,color="midnightblue",fontsize=10,style="solid"];
+						if m.caller_name == 'main.main' {
+							m.sb.writeln('\t$m.dot_caller_name -> $dot_called_name [color="blue"];')
+						} else {
+							m.sb.writeln('\t$m.dot_caller_name -> $dot_called_name')
+						}
+					}
+				}
+				else {}
+			}
+		}
+		else {}
+	}
+}
+
+/*
+mut fpath := ''
+	if m.file != 0 {
+		fpath = m.file.path
+	}
+	node_pos := node.position()
+	fpos := '$fpath:$node_pos.line_nr:$node_pos.col:'
+	println('$fpos $node.type_name() | $node')
+*/
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index b8d65c1531..d217734769 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -9,7 +9,7 @@ import v.util
 fn (mut g Gen) is_used_by_main(node ast.FnDecl) bool {
 	mut is_used_by_main := true
 	if g.pref.skip_unused {
-		fkey := if node.is_method { '${int(node.receiver.typ)}.$node.name' } else { node.name }
+		fkey := node.fkey()
 		is_used_by_main = g.table.used_fns[fkey]
 		$if trace_skip_unused_fns ? {
 			println('> is_used_by_main: $is_used_by_main | node.name: $node.name | fkey: $fkey | node.is_method: $node.is_method')
@@ -21,8 +21,7 @@ fn (mut g Gen) is_used_by_main(node ast.FnDecl) bool {
 		}
 	} else {
 		$if trace_skip_unused_fns_in_c_code ? {
-			fkey := if node.is_method { '${int(node.receiver.typ)}.$node.name' } else { node.name }
-			g.writeln('// trace_skip_unused_fns_in_c_code, $node.name, fkey: $fkey')
+			g.writeln('// trace_skip_unused_fns_in_c_code, $node.name, fkey: $node.fkey()')
 		}
 	}
 	return is_used_by_main
diff --git a/vlib/v/gen/native/amd64.v b/vlib/v/gen/native/amd64.v
index af1bf1d168..2e945b050e 100644
--- a/vlib/v/gen/native/amd64.v
+++ b/vlib/v/gen/native/amd64.v
@@ -721,7 +721,7 @@ pub fn (mut g Gen) call_fn(node ast.CallExpr) {
 	if !n.contains('.') {
 		n = 'main.$n'
 	}
-	println('call fn ($n)')
+	eprintln('call fn ($n)')
 	addr := g.fn_addr[n]
 	if addr == 0 {
 		verror('fn addr of `$name` = 0')
diff --git a/vlib/v/markused/markused.v b/vlib/v/markused/markused.v
index 0743eb3718..2d911394f6 100644
--- a/vlib/v/markused/markused.v
+++ b/vlib/v/markused/markused.v
@@ -351,11 +351,7 @@ fn all_fn_and_const(ast_files []&ast.File) (map[string]ast.FnDecl, map[string]as
 		for node in file.stmts {
 			match node {
 				ast.FnDecl {
-					fkey := if node.is_method {
-						'${int(node.receiver.typ)}.$node.name'
-					} else {
-						node.name
-					}
+					fkey := node.fkey()
 					all_fns[fkey] = node
 				}
 				ast.ConstDecl {
diff --git a/vlib/v/markused/walker.v b/vlib/v/markused/walker.v
index e2c244f893..4031589ae9 100644
--- a/vlib/v/markused/walker.v
+++ b/vlib/v/markused/walker.v
@@ -377,7 +377,7 @@ pub fn (mut w Walker) fn_decl(mut node ast.FnDecl) {
 	if node.language == .c {
 		return
 	}
-	fkey := if node.is_method { '${int(node.receiver.typ)}.$node.name' } else { node.name }
+	fkey := node.fkey()
 	if w.used_fns[fkey] {
 		// This function is already known to be called, meaning it has been processed already.
 		// Save CPU time and do nothing.
@@ -398,11 +398,7 @@ pub fn (mut w Walker) call_expr(mut node ast.CallExpr) {
 	w.expr(node.left)
 	w.or_block(node.or_block)
 	//
-	fn_name := if node.is_method {
-		int(node.receiver_type).str() + '.' + node.name
-	} else {
-		node.name
-	}
+	fn_name := node.fkey()
 	if w.used_fns[fn_name] {
 		return
 	}