Exercise: construct the SLR parsing table for grammar:

1

• Exercise construct the SLR parsing table for
  grammar
• S-gtLR,
• S-gtR
• L-gtR
• L-gtid
• R-gtL
• The grammar can have shift/reduce conflict or
  reduce/reduce conflict.
• What about shift/shift conflict?

2

• SLR does not always remember the right context --
  using the follow set to determine when to reduce
  is sometimes too general.
• LR(1) parsing table has more context information
  in its items.
• An LR(1) item is of the form
• terminal a has not effect when is not .
  
• When is , an item of the form
  means to reduce only when the next input
  symbol is a.

3

• Computing sets of LR(1) items.
• Closure(I) is now slightly different
• Start the construction of the set of LR(1) items
  by computing the closure of

4

• Example 1 first page
• Example 2
• S -gt S
• S -gt CC
• C -gtcC
• C -gtd

5

• Constructing the LR(1) parsing table

6

• The number of states in LR(1) parsing table is
  much more than that in SLR parsing table.
• LALR reduces the number of states in LR(1)
  parsing table.
• LALR (LookAhead LR) is less powerful than LR(1)
• reducing states may introduce reduce-reduce
  conflict, but not shift-reduce conflict.
• LALR has the same number of states as SLR, but
  more powerful.
• Constructing LALR parsing table.
• Combine LR(1) sets with the same sets of first
  parts (ignore lookahead).
• Algorithms exist that skip constructing the LR(1)
  sets.

7

• Using ambiguous grammars
• ambiguous grammars will results in conflicts
• Can use precedence and assocativity to resolve
  the conflicts
• May result in a smaller parsing table in
  comparison to using un-ambiguous grammars.
• Example
• E-gtEE
• E-gtEE
• E-gt(E)
• E-gtid