LALR(1) Parsing

• Sometimes, in specific states not all terminals from follow(X) can really occur.
• Idea: Propagate state-specific follow symbols.
• Reduce only if the symbol is in the state specific follow symbols.
• The resulting parser is called LALR(1) for Look-Ahead-LR.
• The number of states is the same as in LR(0) and SLR.
• This is, what JavaCUP uses (also yacc, bison).
• If an LALR(1) parser generator gives a conflict, then for all practical purposes it cannot know, what to do in certain situations.