SYNOPSIS

This is an example of a bad grammar design.

There are several sources of ambiguity in this grammar:

• Statments like

  NUM NUM NUM

  are ambiguous. The following two left-most derivations exists:

              s =*=> ns ns =*=> NUM NUM ns => NUM NUM NUM
  or 
  
              s =*=> ns ns =*=> NUM ns =*=> NUM NUM NUM

  the same with phrases like ID ID ID

• The empty word can be generated in many ways

  s => empty

  or

  s => s ns => s empty => empty

  etc.

Compile it with

eyapp -b '' typicalrr

The compiler will announce:

3 shift/reduce conflicts and 3 reduce/reduce conflicts

Study the file typicalrr.output. The 3 reduce/reduce conflicts occur in state 1:

  State 1:

	$start -> s . $end	(Rule 0)
	s -> s . ws	(Rule 2)
	s -> s . ns	(Rule 3)

	$end	shift, and go to state 3

	$end	[reduce using rule 6 (ws)]
	$end	[reduce using rule 4 (ns)]
	ID	[reduce using rule 6 (ws)]
	NUM	[reduce using rule 6 (ws)]
	$default	reduce using rule 4 (ns)

	ns	go to state 2
	ws	go to state 4

        Rules:
        ------
        0:	$start -> s $end
        1:	s -> /* empty */
        2:	s -> s ws
        3:	s -> s ns
        4:	ns -> /* empty */
        5:	ns -> ns NUM
        6:	ws -> /* empty */
        7:	ws -> ws ID

Execute it with:

./typicalrr.pm -d

Try inputs 4 5, a b and 4 5 a b.

SEE ALSO

For a solution to the conflicts see correcttypicalrr.eyp and typicalrr_fixed.eyp