Update parser.py

parser.py

 def preprocess():
 
 # Return the next token from the input
-def getToken():
-    int lastChar = ' '
-    for c in input:
-        lastChar = c if c != ' '
+def lex(input):
+    tokens = []
+    
+    while len(input.split()):
+        if input is not None:
+            continue
+        
+        if input[0] in ingredients:
+            input = input[1:]
+        else:
+            raise Exception('Don\'t know what this is: {}'.format(input[0]))
 
 def parse():
-    preprocess():
-    tokenise()
+    preprocess()
+    lex(input)
     isValid()
\ No newline at end of file