feat: Add numbers and arithmetic operations

examples/arithmetic.fem

@@ -0,0 +1,3 @@
+my_number is 10 + 5 * 2
+UwU Boy my_number
+UwU Boy 20 / 4 - 1

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")

src/lexer.py

@@ -38,6 +38,25 @@ class Lexer:
             self.pos = string_end + 1
             return Token('STRING', string)
 
+        if current_char.isdigit():
+            start_pos = self.pos
+            while self.pos < len(self.text) and self.text[self.pos].isdigit():
+                self.pos += 1
+            return Token('INTEGER', int(self.text[start_pos:self.pos]))
+
+        if current_char == '+':
+            self.pos += 1
+            return Token('PLUS', '+')
+        if current_char == '-':
+            self.pos += 1
+            return Token('MINUS', '-')
+        if current_char == '*':
+            self.pos += 1
+            return Token('MUL', '*')
+        if current_char == '/':
+            self.pos += 1
+            return Token('DIV', '/')
+
         # Match keywords
         if re.match(r'\bUwU Boy\b', self.text[self.pos:]):
             self.pos += 7

src/parser.py

@@ -1,6 +1,17 @@
 class AST:
     pass
 
+class Number(AST):
+    def __init__(self, token):
+        self.token = token
+        self.value = token.value
+
+class BinOp(AST):
+    def __init__(self, left, op, right):
+        self.left = left
+        self.token = self.op = op
+        self.right = right
+
 class Print(AST):
     def __init__(self, value):
         self.value = value
@@ -48,19 +59,19 @@ class Parser:
         if token.type == 'ID' and self.pos + 1 < len(self.tokens) and self.tokens[self.pos + 1].type == 'ASSIGN':
             return self.parse_assignment_statement()
         elif token.type == 'ID':
-            raise Exception(f"Unexpected identifier '{token.value}' without assignment.")
+            # This case should be handled by expression parsing if it's part of an expression
+            # For now, raise an error if it's a standalone ID not part of assignment or print
+            raise Exception(f"Unexpected identifier '{token.value}' without assignment or print.")
 
+        # Handle expressions as statements (e.g., just a number or an arithmetic operation)
+        # This might need refinement depending on what we consider a valid standalone statement
+        # For now, let's assume expressions are only part of print or assignment
         raise Exception(f"Invalid statement starting with token {token.type}")
 
     def parse_print_statement(self):
         self.get_next_token()  # Consume PRINT token
-        token = self.get_next_token()
-        if token.type == 'STRING':
-            return Print(token.value)
-        elif token.type == 'ID':
-            return Print(Variable(token))
-        else:
-            raise Exception("Expected a string or variable after 'UwU Boy'")
+        expr = self.expression()
+        return Print(expr)
 
     def parse_assignment_statement(self):
         var_token = self.get_next_token()
@@ -68,8 +79,30 @@ class Parser:
         
         assign_token = self.get_next_token()
 
-        value_token = self.get_next_token()
-        if value_token.type == 'STRING':
-            return Assign(left=var_node, op=assign_token, right=value_token.value)
+        right_expr = self.expression()
+        return Assign(left=var_node, op=assign_token, right=right_expr)
+
+    def factor(self):
+        token = self.get_next_token()
+        if token.type == 'INTEGER':
+            return Number(token)
+        elif token.type == 'STRING':
+            return token.value # Strings are literals, not AST nodes for now
+        elif token.type == 'ID':
+            return Variable(token)
         else:
-            raise Exception("Expected a string value for assignment")
+            raise Exception(f"Expected integer, string or identifier, got {token.type}")
+
+    def term(self):
+        node = self.factor()
+        while self.peek_next_token().type in ('MUL', 'DIV'):
+            token = self.get_next_token()
+            node = BinOp(left=node, op=token, right=self.factor())
+        return node
+
+    def expression(self):
+        node = self.term()
+        while self.peek_next_token().type in ('PLUS', 'MINUS'):
+            token = self.get_next_token()
+            node = BinOp(left=node, op=token, right=self.term())
+        return node