Top-Down Parsing

Consider the CFG with productions:

expr → term rest
rest  → + term rest | - term rest
term → 0 | 1 | . . . | 9

Step 0:

Initialization: Root must be starting symbol

Step 1:

expr → term rest

Step 2:

term → 9

Step 3

rest → term rest

Step 4:

term → 5

Step 5:

rest → term rest

Step 6:

term → 2

Step 7:

rest → E

In the example above, the grammar made it easy for the top-down parser to pick the correct production in each step.
This is not true in general, see example of dangling 'else'.