Editing LR parser (section)

=== Action and goto tables ===

The two LR(0) parsing tables for this grammar look as follows:

{| class=wikitable
|-  style="text-align:center; background:#e0e0e0;"
| '''''state'''''
| colspan="5"|'''''action'''''
| colspan="2"|'''''goto'''''
|- style="text-align:center;"
| style="width:12%;"|&nbsp;
|  style="width:11%; background:#d0e0ff;"|'''*'''
|  style="width:11%; background:#d0e0ff;"|'''+'''
|  style="width:11%; background:#d0e0ff;"|'''0'''
|  style="width:11%; background:#d0e0ff;"|'''1'''
|  style="width:11%; background:#d0e0ff;"|'''$'''
|  style="width:11%; background:#c0e0d0;"|'''E'''
|  style="width:11%; background:#c0e0d0;"|'''B'''
|- style="text-align:center;"
| '''0''' || &nbsp; || &nbsp; || s1     || s2    || &nbsp; ||  3     || 4
|- style="text-align:center;"
| '''1''' || r4     || r4     || r4     || r4     || r4     || &nbsp; || &nbsp;
|- style="text-align:center;"
| '''2''' || r5     || r5     || r5     || r5     || r5     || &nbsp; || &nbsp;
|- style="text-align:center;"
| '''3''' || s5     || s6     || &nbsp; || &nbsp; || acc    || &nbsp; || &nbsp;

|- style="text-align:center;"
| '''4''' || r3     || r3     || r3     || r3     || r3     || &nbsp; || &nbsp;
|- style="text-align:center;"
| '''5''' || &nbsp; || &nbsp; || s1     || s2     || &nbsp; || &nbsp; || 7
|- style="text-align:center;"
| '''6''' || &nbsp; || &nbsp; || s1     || s2     || &nbsp; || &nbsp; || 8
|- style="text-align:center;"
| '''7''' || r1     || r1     || r1     || r1     || r1     || &nbsp; || &nbsp;
|- style="text-align:center;"
| '''8''' || r2     || r2     || r2     || r2     || r2     || &nbsp; || &nbsp;
|}

The '''action table''' is indexed by a state of the parser and a terminal (including a special terminal $ that indicates the end of the input stream) and contains three types of actions:
* ''shift'', which is written as "s''n''" and indicates that the next state is ''n''
* ''reduce'', which is written as "r''m''" and indicates that a reduction with grammar rule ''m'' should be performed
* ''accept'', which is written as "acc" and indicates that the parser accepts the string in the input stream.

The '''goto table''' is indexed by a state of the parser and a nonterminal and simply indicates what the next state of the parser will be if it has recognized a certain nonterminal. This table is important to find out the next state after every reduction. After a reduction, the next state is found by looking up the '''goto table''' entry for top of the stack (i.e. current state) and the reduced rule's LHS (i.e. non-terminal).