Elsif Hints

Steps to adding ELSIF to your grammar:

Implement if/else using matched/unmatched. Test.
Incorporate while in the matched/unmatched productions. This means creating both a matched and an unmatched version of while. Test.
Incorporate loop in the matched/unmatched productions. This means creating both a matched and an unmatched version of loop. Test.
Now link in the elsif stuff by adding to the list of possible matched statements:
```
             | IF simpleExp THEN matched matchedelsifs
```
and to the unmatched statements something like:
```
 IF simpleExp THEN matched unmatchedelsifs
```
This will connect to two new nonterminals matchedelsifs and unmatchedelsifs.
For matchedelsifs create productions that add one or more ELSIFs. They need things that look like:
```
ELSIF simpleExp THEN matched ELSIF simpleExp THEN matched ELSIF simpleExp THEN matched ...
```
This list of elsifs must end in an: ELSE matched to match the elsif.
Similarly add productions for unmatchedelsifs which is again a list of ELSIFs like above but can end in one of two ways that are unmatched. See what were unmatched things in the unmatched code you already wrote for a hint.