| Removal of left recursion
Suppose we have translation scheme:
A  A1 Y |
{A = g(A 1 ,Y)}
|
| A X |
{A = f(X)}
|
After removal of left recursion it becomes
| A X |
{R.in = f(X)}
|
| R |
{A.s =R.s}
|
| R Y |
{R1 .in = g(Y,R)}
|
| R1 |
{R.s = R1 .s}
|
| R ε |
{R.s = R.i}
|
The general scheme for transforming left-recursive translation for predictive parsing is shown below:
Suppose we have the following translation scheme :
| A -> A1Y |
{A.s = g(A1.s, Y.s)}
|
| A -> X |
{A.s = f(X.s)}
|
Each grammar symbol has a synthesized attribute written using the lower case letter s. (f and g are arbitrary functions.)
After removing left recursion from the above grammar and taking semantic actions into account, the transformed scheme becomes:
| A -> X |
{R.in = f(X.s)}
|
| R |
{A.s = R.s}
|
| R -> Y
|
{R1.in = g(Y.s,R.in)} |
| R1 |
{R.s = R1.s}
|
| R ->ε |
{R.s = R.in}
|
| |
|
|
