diff --git a/src/formulate/_utils.py b/src/formulate/_utils.py
index 8b6be10..dec860f 100644
--- a/src/formulate/_utils.py
+++ b/src/formulate/_utils.py
@@ -5,7 +5,8 @@
 """
 from __future__ import annotations
 
-import lark
+from . import numexpr_parse
+from . import  ttreeformula_parser
 
 UNARY_OP = {"pos", "neg", "binv", "linv"}
 with_sign = {}
@@ -34,16 +35,15 @@
 }
 
 
-def _ptree_to_string(exp_tree: lark.tree.Tree, out_exp: list):
-    # print("==================================")
-    # print(exp_tree)
-    # print("==================================")
-    if isinstance(exp_tree, lark.lexer.Token):
+def _ptree_to_string(exp_tree, out_exp: list):
+    if isinstance(exp_tree, numexpr_parser.Token) or isinstance(exp_tree, ttreeformula_parser.Token):
         out_exp.append(str(exp_tree))
         return out_exp
+
     elif exp_tree is None:
         return out_exp
-    elif isinstance(exp_tree.data, lark.lexer.Token):
+
+    elif isinstance(exp_tree.data, numexpr_parser.Token) or isinstance(exp_tree.data, ttreeformula_parser.Token):
         cur_type = exp_tree.data.type
         cur_val = exp_tree.data.value
         children = exp_tree.children
@@ -64,9 +64,9 @@ def _ptree_to_string(exp_tree: lark.tree.Tree, out_exp: list):
                 out_exp.append(val_to_sign[cur_val])
                 out_exp.extend(_ptree_to_string(children[1], []))
                 out_exp.append(")")
+
     else:
         children = exp_tree.children
-        print(exp_tree.data)
         # print(exp_tree, "adwe")
         if exp_tree.data in UNARY_OP:
             child = exp_tree.children[0]
@@ -75,45 +75,54 @@ def _ptree_to_string(exp_tree: lark.tree.Tree, out_exp: list):
             out_exp.extend(_ptree_to_string(child, []))
             out_exp.append(")")
             return out_exp
+
         if len(children) == 1 and (
             children[0].type == "CNAME" or children[0].type == "NUMBER"
         ):
             # print(str(children[0]))
             out_exp.append(str(children[0]))
             return out_exp
+
         if exp_tree.data == "func":
             children = exp_tree.children
             head = children[0]
             tail = children[1]
             pre_name = head.children[0]
             out_exp.append(str(pre_name))
+
             if len(head.children) > 1:
                 subchild = head.children[1]
-                while not isinstance(subchild, lark.lexer.Token):
+
+                while not (isinstance(subchild, numexpr_parser.Token) or isinstance(subchild, ttreeformula_parser.Token)):
                     out_exp.append("::")
                     out_exp.append(str(subchild.children[0]))
+
                     if len(subchild.children) > 1:
                         subchild = subchild.children[1]
                     else:
                         break
-                print(out_exp)
 
-            print(out_exp, "gfege")
             out_exp.append("(")
             out_exp.extend(_ptree_to_string(tail, []))
             out_exp.append(")")
             return out_exp
+            
         if exp_tree.data != "matr":
             out_exp.append("(")
         out_exp.extend(_ptree_to_string(children[0], []))
+
         for i in range(1, len(children)):
+
             if exp_tree.data == "matr":
                 out_exp.append("[")
+
             else:
                 out_exp.append(val_to_sign[exp_tree.data])
             out_exp.extend(_ptree_to_string(children[i], []))
+
             if exp_tree.data == "matr":
                 out_exp.append("]")
+                
         if exp_tree.data != "matr":
             out_exp.append(")")
     return out_exp
diff --git a/src/formulate/matching_tree.py b/src/formulate/matching_tree.py
index 04f3a3b..b6ed337 100644
--- a/src/formulate/matching_tree.py
+++ b/src/formulate/matching_tree.py
@@ -5,7 +5,6 @@
 """
 
 
-import lark
 from . import numexpr_parser
 from . import ttreeformula_parser