5.2.3 Shift-Reduce Conflicts

If the grammar is not SLR(1), then there may be more than one entry in the table. If both a "shift" action and "reduce" action occur in the same entry, and the parsing process consults that entry, then a shift-reduce conflict is said to occur (see Exercise 7). Briefly, a shift-reduce error occurs when the parser cannot decide whether to continue shifting or to reduce (using a different production rule).

Similarly, a reduce-reduce error occurs when the parser has to choose between more than one equally acceptable production.

One way to resolve such conflicts is to attempt to rewrite the grammar. Another method is to analyze the situation and decide, if possible, which action is the correct one. If neither of these steps solve the problem, then it is possible that the underlying language construct cannot be described using an SLR(1) grammar; a different method will have to be used.