1. UMBC CMSC 331 ONLINE LECTURE 3
SD Vick

2. Mini Lectures
Left Recursion defined and explained with and caveats (see _Rem_1.swf)
Left recursion removal example (see _rem_2.swf)
(Full text of mini-lectures )

3. What’s the General Rule?
A -> A a1 | A a2 | … A am | b1 | b2 | bn
________________________________________
A-> b1 A’ | b2 A’ … bn A’
A’ -> a1 A’ | a2 A’ | … am A’ | e

4. Removing Left Recursion
Consider the following Grammar
<z> -> <w>  ? <x> |
<z> ! <y> |
a <z>
<x> -> <z> * <x> |
<x> / <y> |
<w>
<w> -> e | f
Why is this Left Recursive?
Now we must just pick our a’s and our b’s

5. The Mechanics <z> -> <w> ? <x> |
<z> ! <y> |
a <z>
<z> -> <w>  ? <x> <z’> |
a <z> <z’>
<z’> -> ! <y> <z’> | e b1 a1 b2
Try the second rule on your own
Here we have 2 b‘s and 1 a, what if the situation was reversed?