LLparse and LRparse: visual and interactive tools for parsing

This paper describes instructional tools, LLparse and LRparse, for visualizing and interacting with small examples of LL and LR parsing. These tools can be used to understand the process of constructing LL(1) and LR(1) parse tables through a series of steps in which users receive feedback on the correctness of each step before moving on to the next step. For example, in LRparse, the user initially enters an LR(1) grammar, calculates FIRST and FOLLOW sets, graphically constructs a deterministic finite automation of item sets, and finally constructs the LR(1) parsing table. Upon completion of the constructed table, the user can observe a visualization of the parsing of input strings. These tools can be used to provide problem solving feedback in courses on automata theory or computer design.