diff --git a/pyrimidine/errors.py b/pyrimidine/errors.py
index ad916d2..c20791f 100755
--- a/pyrimidine/errors.py
+++ b/pyrimidine/errors.py
@@ -5,16 +5,26 @@ class UnknownSizeError(Exception):
 
     def __init__(self, cls):
         self.cls = cls
-        
+
     def __str__(self):
-        return f'The size of `{self.cls}` is unkown, the object could not be generated.'
+        return f'The size of class `{self.cls.__name__}` is unkown, the object could not be generated.'
 
 
 class UnavalibleAttributeError(AttributeError):
-    
+
     def __init__(self, cls, attr_name):
         self.cls = cls
         self.attr_name = attr_name
-        
+
+    def __str__(self):
+        return f'Did not define attribute `{self.attr_name}` for the class `{self.cls.__name__}`.'
+
+
+class RegesterError(AttributeError):
+
+    def __init__(self, cls, attr_name):
+        self.cls = cls
+        self.attr_name = attr_name
+
     def __str__(self):
-        return f'Did not define attribute `{self.attr_name}` for `{self.cls}`.'
\ No newline at end of file
+        return AttributeError(f'`{attr_name}` is an attribute of the class `{self.cls.__name__}`, and would not be redefined.')
diff --git a/pyrimidine/meta.py b/pyrimidine/meta.py
index bb2fd05..20a6c4c 100755
--- a/pyrimidine/meta.py
+++ b/pyrimidine/meta.py
@@ -257,13 +257,22 @@ def _regester_map(self, name, key=None, force=True):
             def m(obj, *args, **kwargs):
                 return obj.map(key, obj.__elements, *args, **kwargs)
             if not force and hasattr(self, name):
-                raise AttributeError(f'`{name}` is an attribute of {self.__class__.__name__}, and would not be regestered.')
+                raise RegesterError(self.__class__, name)
             setattr(self, name, MethodType(m, self))
 
         attrs.update({
             'regester_map': _regester_map
         })
 
+        def _regester(self, name, key, force=True):
+            if not force and hasattr(self, name):
+                raise RegesterError(self.__class__, name)
+            setattr(self, name, MethodType(key, self))
+
+        attrs.update({
+            'regester': _regester
+        })
+
         return super().__new__(cls, name, bases, attrs)
 
     def __call__(self, *args, **kwargs):
diff --git a/tests/test_meta.py b/tests/test_meta.py
index 9cb5298..45d00ff 100644
--- a/tests/test_meta.py
+++ b/tests/test_meta.py
@@ -20,7 +20,7 @@ def after_setter(self):
                 
         C = self.mc
         c = C([UserString('I'), UserString('love'), UserString('you')], lasting='for ever')
-        C.set_methods(n_elems=lambda c: 1)
+        C.set(n_elems=lambda c: 1)
         self.C = C
         self.c = c
 
@@ -41,7 +41,6 @@ def n_vowels(s):
         c.regester_map('length', n_vowels)
         assert list(c.length()) == [1, 2, 2]
 
-
     def test_subclass(self):
         C = self.C
         class D(C):