Variable __init__ en __str__ werken

main.py

@@ -19,11 +19,13 @@ class LambdaTerm:
 class Variable(LambdaTerm):
     """Represents a variable."""
 
-    def __init__(self, symbol): raise NotImplementedError
+    def __init__(self, symbol): 
+        self.symbol = symbol
 
     def __repr__(self): raise NotImplementedError
 
-    def __str__(self): raise NotImplementedError
+    def __str__(self): 
+        return str(self.symbol)
 
     def substitute(self, rules): raise NotImplementedError
 
@@ -54,3 +56,5 @@ class Application(LambdaTerm):
     def substitute(self, rules): raise NotImplementedError
 
     def reduce(self): raise NotImplementedError
+
+print(str(Variable('x')))
\ No newline at end of file