feat: Add numbers and arithmetic operations

src/interpreter.py

@@ -1,6 +1,7 @@
 class Interpreter:
     def __init__(self, ast):
         self.ast = ast
+        self.variables = {}
 
     def interpret(self):
         for node in self.ast:
@@ -14,5 +15,31 @@ class Interpreter:
     def no_visit_method(self, node):
         raise Exception(f'No visit_{type(node).__name__} method defined')
 
+    def visit_Number(self, node):
+        return node.value
+
+    def visit_BinOp(self, node):
+        if node.op.type == 'PLUS':
+            return self.visit(node.left) + self.visit(node.right)
+        elif node.op.type == 'MINUS':
+            return self.visit(node.left) - self.visit(node.right)
+        elif node.op.type == 'MUL':
+            return self.visit(node.left) * self.visit(node.right)
+        elif node.op.type == 'DIV':
+            return self.visit(node.left) / self.visit(node.right)
+
     def visit_Print(self, node):
-        print(node.value)
+        value_to_print = self.visit(node.value)
+        print(value_to_print)
+
+    def visit_Assign(self, node):
+        var_name = node.left.value
+        value = self.visit(node.right)
+        self.variables[var_name] = value
+
+    def visit_Variable(self, node):
+        var_name = node.value
+        if var_name in self.variables:
+            return self.variables[var_name]
+        else:
+            raise NameError(f"name '{var_name}' is not defined")