diff --git a/Makefile b/Makefile
index 03f054f..083b0b2 100644
--- a/Makefile
+++ b/Makefile
@@ -17,7 +17,7 @@ relational_gui/resources.py:
 
 .PHONY: mypy
 mypy:
-	mypy relational
+	mypy relational relational_readline
 
 .PHONY: test
 test:
diff --git a/relational/relation.py b/relational/relation.py
index d9f1703..8c8d1a6 100644
--- a/relational/relation.py
+++ b/relational/relation.py
@@ -134,7 +134,7 @@ class Relation(NamedTuple):
         try:
             c_expr = compile(expr, 'selection', 'eval')
         except:
-            raise Exception('Failed to compile expression: %s' % expr)
+            raise Exception(f'Failed to compile expression: {expr}')
 
         content = []
         for i in self.content:
@@ -147,8 +147,7 @@ class Relation(NamedTuple):
                 if eval(c_expr, attributes):
                     content.append(i)
             except Exception as e:
-                raise Exception(
-                    "Failed to evaluate %s\n%s" % (expr, e.__str__()))
+                raise Exception(f'Failed to evaluate {expr}\n{e}')
         return Relation(header, frozenset(content))
 
     def product(self, other: 'Relation') -> 'Relation':
@@ -403,7 +402,7 @@ class Header(tuple):
 
         for i in self:
             if not is_valid_relation_name(i):
-                raise Exception('"%s" is not a valid attribute name' % i)
+                raise Exception(f'"{i}" is not a valid attribute name')
 
         if len(self) != len(set(self)):
             raise Exception('Attribute names must be unique')
@@ -419,12 +418,12 @@ class Header(tuple):
         attrs = list(self)
         for old, new in params.items():
             if not is_valid_relation_name(new):
-                raise Exception('%s is not a valid attribute name' % new)
+                raise Exception(f'{new} is not a valid attribute name')
             try:
                 id_ = attrs.index(old)
                 attrs[id_] = new
             except:
-                raise Exception('Field not found: %s' % old)
+                raise Exception(f'Field not found: {old}')
         return Header(attrs)
 
     def sharedAttributes(self, other: 'Header') -> int:
diff --git a/relational_readline/linegui.py b/relational_readline/linegui.py
index 872c996..8655cac 100644
--- a/relational_readline/linegui.py
+++ b/relational_readline/linegui.py
@@ -27,7 +27,7 @@ from typing import Optional
 
 from relational import relation, parser, rtypes
 from relational import maintenance
-from xtermcolor import colorize
+from xtermcolor import colorize  # type: ignore
 
 PROMPT_COLOR = 0xffff00
 ERROR_COLOR = 0xff0000
@@ -113,7 +113,7 @@ completer = SimpleCompleter(
      '_DIFFERENCE ', '_JOIN ', '_LJOIN ', '_RJOIN ', '_FJOIN ', '_PROJECTION ', '_RENAME_TO ', '_SELECTION ', '_RENAME ', '_DIVISION '])
 
 
-def load_relation(filename: str, defname:Optional[str]=None) -> Optional[str]:
+def load_relation(filename: str, defname: Optional[str]) -> Optional[str]:
     '''
     Loads a relation into the set. Defname is the given name
     to the relation.
@@ -123,7 +123,7 @@ def load_relation(filename: str, defname:Optional[str]=None) -> Optional[str]:
     '''
     if not os.path.isfile(filename):
         print(colorize(
-            "%s is not a file" % filename, ERROR_COLOR), file=sys.stderr)
+            f'{filename} is not a file', ERROR_COLOR), file=sys.stderr)
         return None
 
     if defname is None:
@@ -137,7 +137,7 @@ def load_relation(filename: str, defname:Optional[str]=None) -> Optional[str]:
             "%s is not a valid relation name" % defname, ERROR_COLOR), file=sys.stderr)
         return None
     try:
-        relations[defname] = relation.Relation(filename)
+        relations[defname] = relation.Relation.load(filename)
 
         completer.add_completion(defname)
         printtty(colorize("Loaded relation %s" % defname, COLOR_GREEN))
@@ -216,10 +216,9 @@ def exec_line(command: str) -> None:
             return
 
         filename = pars[1]
+        defname = None
         if len(pars) > 2:
             defname = pars[2]
-        else:
-            defname = None
         load_relation(filename, defname)
 
     elif command.startswith('UNLOAD '):
@@ -320,7 +319,7 @@ def main(files=[]):
            "; Completion is activated using the tab (if supported by the terminal)")
 
     for i in files:
-        load_relation(i)
+        load_relation(i, None)
 
     readline.set_completer(completer.complete)