From f3ed00e5f2c3cf9bcda79aa3188cfd638f4e773d Mon Sep 17 00:00:00 2001
From: Garritt McCune <glmccune@gmail.com>
Date: Wed, 22 Apr 2020 02:52:52 -0500
Subject: [PATCH] Added negative number support in the tokenizer.

---
 tokenizer.py | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tokenizer.py b/tokenizer.py
index 92fe785..b4c4a72 100644
--- a/tokenizer.py
+++ b/tokenizer.py
@@ -24,6 +24,17 @@ def get_tokens_from_expression_string(expression_string):
 			parsing_number = True
 			tmp = tmp + c
 			continue
+		
+		elif c == '-' and not parsing_number:
+			if expression_string[i + 1] == '.' or expression_string[i + 1].isdigit():
+				tmp = "-"
+				parsing_number = True
+			else:
+				tokens.append(token.Token(c, token.TokenType.get_operator(c)))
+				parsing_number = False
+				tmp = ""
+				continue
+		
 		elif c == '(':
 			if parsing_number:
 				tokens.append(token.Token(tmp, token.TokenType.constant))
@@ -50,7 +61,7 @@ def get_tokens_from_expression_string(expression_string):
 			if len(tokens) > 1:
 				lookBehind = tokens[-1]
 				if lookBehind.type == token.TokenType.exp_end:
-					tokens.append(token.Token("^", token.TokenType.power))					
+					tokens.append(token.Token("^", token.TokenType.power))
 					
 			if (i + 1) < len(expression_string):
 				lookAHead = expression_string[i + 1]
@@ -73,6 +84,11 @@ def get_tokens_from_expression_string(expression_string):
 	
 	return tokens
 
+def peek_list(tokens):
+    if tokens:
+        return tokens[-1]
+    else:
+        raise IndexError("The token list is empty.", tokens)
 
 def replace_variables(tokens, new_constants):
 	newTokenList = []