lang: Improve graph shape with speculative execution

Most of the time, we don't need to have a dynamic call sub graph, since
the actual function call could be represented statically as it
originally was before lambda functions were implemented. Simplifying the
graph shape has important performance benefits in terms of both keep the
graph smaller (memory, etc) and in avoiding the need to run transactions
at runtime (speed) to reshape the graph.

Co-authored-by: Samuel Gélineau <gelisam@gmail.com>

lang/parser/lexparse_test.go

@@ -1744,7 +1744,8 @@ func TestLexParse0(t *testing.T) {
 				&ast.StmtFunc{
 					Name: "f1",
 					Func: &ast.ExprFunc{
-						Args: []*interfaces.Arg{},
+						Title: "f1",
+						Args:  []*interfaces.Arg{},
 						Body: &ast.ExprInt{
 							V: 42,
 						},
@@ -1765,6 +1766,7 @@ func TestLexParse0(t *testing.T) {
 	}
 	{
 		fn := &ast.ExprFunc{
+			Title:  "f2",
 			Args:   []*interfaces.Arg{},
 			Return: types.TypeInt,
 			Body: &ast.ExprCall{
@@ -1809,6 +1811,7 @@ func TestLexParse0(t *testing.T) {
 	}
 	{
 		fn := &ast.ExprFunc{
+			Title: "f3",
 			Args: []*interfaces.Arg{
 				{
 					Name: "a",
@@ -1860,6 +1863,7 @@ func TestLexParse0(t *testing.T) {
 	}
 	{
 		fn := &ast.ExprFunc{
+			Title: "f4",
 			Args: []*interfaces.Arg{
 				{
 					Name: "x",
@@ -2048,7 +2052,8 @@ func TestLexParse0(t *testing.T) {
 					Name: "funcgen",
 					// This is the outer function...
 					Func: &ast.ExprFunc{
-						Args: []*interfaces.Arg{},
+						Title: "funcgen",
+						Args:  []*interfaces.Arg{},
 						// This is the inner function...
 						Body: &ast.ExprFunc{
 							Args: []*interfaces.Arg{},

lang/parser/parser.y

@@ -255,9 +255,10 @@ stmt:
 		$$.stmt = &ast.StmtFunc{
 			Name: $2.str,
 			Func: &ast.ExprFunc{
-				Args: $4.args,
-				//Return: nil,
-				Body: $7.expr,
+				Title:  $2.str,
+				Args:   $4.args,
+				Return: nil,
+				Body:   $7.expr,
 			},
 		}
 		locate(yylex, $1, yyDollar[len(yyDollar)-1], $$.stmt)
@@ -266,6 +267,7 @@ stmt:
 |	FUNC_IDENTIFIER IDENTIFIER OPEN_PAREN args CLOSE_PAREN type OPEN_CURLY expr CLOSE_CURLY
 	{
 		fn := &ast.ExprFunc{
+			Title:  $2.str,
 			Args:   $4.args,
 			Return: $6.typ, // return type is known
 			Body:   $8.expr,