February 2022
Beginner to intermediate
572 pages
13h
English
Content preview from An Introduction to Formal Languages and Automata, 7th Edition
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15.4 FOLLOW FUNCTION
Next we define the FOLLOW function. FOLLOW makes use of a special symbol $ that indicates an end-of-string marker. The $ symbol is not a terminal or a variable, but rather it is a special symbol that appears to the immediate right of a string to help determine that all the terminals in an input string have been processed. This is a similar idea to a bottom of stack marker in an npda, which is a special symbol one can look at to see if all the symbols on the stack have been processed.
The FOLLOW function is applied to a variable and calculates the set of terminals or $ that can immediately follow that variable in some sentential form. Note that $ can always follow the start symbol S of a context-free grammar. Suppose
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