feat: Implement variables

examples/variables.fem

@@ -0,0 +1,2 @@
+my_variable is "Hello, again!"
+UwU Boy my_variable

src/lexer.py

@@ -20,11 +20,14 @@ class Lexer:
         if self.pos > len(self.text) - 1:
             return Token('EOF', None)
 
-        current_char = self.text[self.pos]
-
-        if current_char.isspace():
+        # Skip whitespace
+        while self.pos < len(self.text) and self.text[self.pos].isspace():
             self.pos += 1
-            return self.get_next_token()
+
+        if self.pos > len(self.text) - 1:
+            return Token('EOF', None)
+
+        current_char = self.text[self.pos]
 
         if current_char == '"':
             self.pos += 1
@@ -35,9 +38,20 @@ class Lexer:
             self.pos = string_end + 1
             return Token('STRING', string)
 
+        # Match keywords
         if re.match(r'\bUwU Boy\b', self.text[self.pos:]):
             self.pos += 7
             return Token('PRINT', 'UwU Boy')
+        if re.match(r'\bis\b', self.text[self.pos:]):
+            self.pos += 2
+            return Token('ASSIGN', 'is')
+
+        # Match identifiers
+        match = re.match(r'\b[a-zA-Z_][a-zA-Z0-9_]*\b', self.text[self.pos:])
+        if match:
+            value = match.group(0)
+            self.pos += len(value)
+            return Token('ID', value)
 
         self.error()
 

src/main.py

@@ -3,7 +3,7 @@ from parser import Parser
 from interpreter import Interpreter
 
 def main():
-    with open('../examples/hello_world.fem', 'r') as f:
+    with open('../examples/variables.fem', 'r') as f:
         text = f.read()
 
     lexer = Lexer(text)

src/parser.py

@@ -5,6 +5,17 @@ class Print(AST):
     def __init__(self, value):
         self.value = value
 
+class Assign(AST):
+    def __init__(self, left, op, right):
+        self.left = left
+        self.op = op
+        self.right = right
+
+class Variable(AST):
+    def __init__(self, token):
+        self.token = token
+        self.value = token.value
+
 class Parser:
     def __init__(self, tokens):
         self.tokens = tokens
@@ -15,22 +26,50 @@ class Parser:
             token = self.tokens[self.pos]
             self.pos += 1
             return token
-        return None
+        return Token('EOF', None)
+
+    def peek_next_token(self):
+        if self.pos < len(self.tokens):
+            return self.tokens[self.pos]
+        return Token('EOF', None)
 
     def parse(self):
         statements = []
-        while True:
-            token = self.get_next_token()
-            if token is None or token.type == 'EOF':
-                break
+        while self.peek_next_token().type != 'EOF':
+            statements.append(self.parse_statement())
+        return statements
+
+    def parse_statement(self):
+        token = self.peek_next_token()
 
         if token.type == 'PRINT':
-                next_token = self.get_next_token()
-                if next_token.type == 'STRING':
-                    statements.append(Print(next_token.value))
-                else:
-                    raise Exception("Expected a string after 'UwU Boy'")
-            else:
-                raise Exception(f"Unexpected token: {token.type}")
+            return self.parse_print_statement()
 
-        return statements
+        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.")
+
+        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'")
+
+    def parse_assignment_statement(self):
+        var_token = self.get_next_token()
+        var_node = Variable(var_token)
+        
+        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)
+        else:
+            raise Exception("Expected a string value for assignment")