diff --git a/bigraph_schema/type_functions.py b/bigraph_schema/type_functions.py
index ff406c4..6bcd7cc 100644
--- a/bigraph_schema/type_functions.py
+++ b/bigraph_schema/type_functions.py
@@ -76,7 +76,7 @@
 from typing import NewType, Union, Mapping, List, Dict, Optional, Callable
 from dataclasses import field, make_dataclass
 
-from bigraph_schema.units import units
+from bigraph_schema.units import units, render_units_type
 from bigraph_schema.registry import (
     NONE_SYMBOL, type_schema_keys,
     is_schema_key, non_schema_keys, type_parameter_key,
@@ -2520,11 +2520,57 @@ def read_shape(shape):
             shape)])
 
 
+# handling unit registration
+# TODO -- can this be done onto the dicts, rather than using the core?
+def register_units(core, units):
+    for unit_name in units._units:
+        try:
+            unit = getattr(units, unit_name)
+        except:
+            # print(f'no unit named {unit_name}')
+            continue
+
+        dimensionality = unit.dimensionality
+        type_key = render_units_type(dimensionality)
+        if not core.exists(type_key):
+            core.register(type_key, {
+                '_default': '',
+                '_apply': apply_units,
+                '_check': check_units,
+                '_serialize': serialize_units,
+                '_deserialize': deserialize_units,
+                '_description': 'type to represent values with scientific units'})
+
+    return core
+
+
+# function to add the unit types to the type library
+def add_units_to_library(units, type_library):
+    for unit_name in units._units:
+        try:
+            unit = getattr(units, unit_name)
+        except AttributeError:
+            continue
+
+        dimensionality = unit.dimensionality
+        type_key = render_units_type(dimensionality)
+        if type_key not in type_library:
+            type_library[type_key] = {
+                '_type': 'unit',
+                'name': unit_name,
+                'dimensionality': str(dimensionality)
+            }
+
+    return type_library
+
 # ===============================
 # Types with their type functions
 # ===============================
 # These dictionaries define the types and their corresponding type functions.
 
+unit_types = {}
+unit_types = add_units_to_library(units, unit_types)
+
 registry_types = {
     'any': {
         '_type': 'any',
@@ -2735,3 +2781,4 @@ def read_shape(shape):
         '_description': 'hyperedges in the bigraph, with inputs and outputs as type parameters',
         'inputs': 'wires',
         'outputs': 'wires'}}
+
diff --git a/bigraph_schema/type_system.py b/bigraph_schema/type_system.py
index 6b76fd3..6743ceb 100644
--- a/bigraph_schema/type_system.py
+++ b/bigraph_schema/type_system.py
@@ -8,15 +8,15 @@
 import functools
 import inspect
 import random
+import traceback
 from pprint import pformat as pf
 
 from bigraph_schema import Registry, non_schema_keys, is_schema_key, deep_merge, type_parameter_key
 from bigraph_schema.parse import parse_expression
 from bigraph_schema.registry import type_schema_keys, remove_omitted, set_path, transform_path
-from bigraph_schema.type_functions import set_apply, registry_types, base_type_library, register_base_reactions, \
-    union_keys, is_empty, \
-    apply_schema, apply_units, check_units, serialize_units, deserialize_units
-from bigraph_schema.units import units, render_units_type
+from bigraph_schema.type_functions import set_apply, registry_types, base_type_library, unit_types, register_base_reactions, \
+    union_keys, is_empty, apply_schema, register_units
+from bigraph_schema.units import units
 
 
 TYPE_FUNCTION_KEYS = [
@@ -107,7 +107,9 @@ def __init__(self):
 
         self.register_types(registry_types)
         self.register_types(base_type_library)
+        # self.register_types(unit_types)
 
+        # # TODO -- add a proper registration into registry
         register_units(self, units)
         register_base_reactions(self)
 
@@ -211,7 +213,6 @@ def register(self, key, schema, alternate_keys=tuple(), force=False):
                     else:
                         lookup = self.find(subschema)
                         if lookup is None:
-                            import ipdb; ipdb.set_trace()
                             raise Exception(
                                 f'trying to register a new type ({key}), '
                                 f'but it depends on a type ({subkey}) which is not in the registry')
@@ -2060,25 +2061,3 @@ def compose(self, a, b):
     def query(self, schema, instance, redex):
         subschema = {}
         return subschema
-
-
-def register_units(core, units):
-    for unit_name in units._units:
-        try:
-            unit = getattr(units, unit_name)
-        except:
-            # print(f'no unit named {unit_name}')
-            continue
-
-        dimensionality = unit.dimensionality
-        type_key = render_units_type(dimensionality)
-        if not core.exists(type_key):
-            core.register(type_key, {
-                '_default': '',
-                '_apply': apply_units,
-                '_check': check_units,
-                '_serialize': serialize_units,
-                '_deserialize': deserialize_units,
-                '_description': 'type to represent values with scientific units'})
-
-    return core