Editing LR parser (section)

=== Extension of Item Set by expansion of non-terminals ===

An item with a dot before a nonterminal, such as E → E + <big>{{color|#f7f|•}}</big> B, indicates that the parser expects to parse the nonterminal B next.  To ensure the item set contains all possible rules the parser may be in the midst of parsing, it must include all items describing how B itself will be parsed.  This means that if there are rules such as B → 1 and B → 0 then the item set must also include the items B → <big>{{color|#f7f|•}}</big> 1 and B → <big>{{color|#f7f|•}}</big> 0. In general this can be formulated as follows:

: If there is an item of the form ''A'' → ''v'' <big>{{color|#f7f|•}}</big> ''Bw'' in an item set and in the grammar there is a rule of the form ''B'' → ''w' '' then the item ''B'' → <big>{{color|#f7f|•}}</big> ''w' '' should also be in the item set.