l rparser edos
DESCRIPTION
Aho, UllmanTRANSCRIPT
LR Parsers
Canonical Collection LR
LR Parser1
Tokens
•Driver Routine
STACK
Prg Ejem1 ; Real X2
Fig. 6.2 Aho, Ullman. “Principles of Compiler Design” pág. 199
ParsingTable
eof…
Driver Routine
Determines Sn, the state on top of stack
Uses the current token ai
Consults Table[Sn , ai ] Edo .Shift sReduceAcceptError
Shift
The parser executes a shift move:
Stack EdoShifts the current token
Reduce
Consults the specific production: A ß If n is the lenght of ß Pop n symbols off the stack Push A onto the stack Note: the current token is not changed in a
reduce move
Accept
IF Table[Sn , ai] = accept, parsing is completed
Error
IF Table[Sn , ai] = error, the parser has discovered an error and calls an error recovery routine
How to construct a simple LR2
Procedure Closure(P)Begin repeat for each item A@♥Bß in P and each production B ¥ in G such that B ♥ ¥ is not in P do add B ♥ ¥ to P until no more items can be aded to P; return P;end
IBID. Fig. 6.5 pág. 207
How to construct a simple LR2
Procedure ITEMS(G’)Begin
C := {CLOSURE(S’ ♥S)};
repeat
for each set of items P in C and each grammar symbol X
such that GOTO(P,X) is not empty and is not in C
do add GOTO(P,X) to C
until no more sets of items can be added to C
end
IBID. Fig. 6.5 pág. 207
Example: G is a grammar with start symbol E
EE + TETTT/FTFF(E)Fid
G’ is the augmented grammar with a new start symbol E’
E’ EEE + TETTT/FTFF(E)Fid
Blue nucleous
Closure(E’)
E’♥E
Blue nucleous
Closure(E)
E’♥EE♥E + TE♥T
Closure(T)
E’♥EE♥E + TE♥TT♥T/FT♥F
Closure(F)
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
State 1
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
State 2=GoTo(1,E)
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
State 3 =GoTo(1,T)
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
State 4=GoTo(1,F)
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
State 5: from state 1 with (
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
F(♥E)E♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
State 6:from state1 with id
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
F(♥E)E♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
Fid♥
States 1,2 ,3,4,5,6
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
F(♥E)E♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
Fid♥
States 7,8,9
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
F(♥E)E♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
Fid♥
E’E+♥TT♥T/FT♥FF♥(E)F♥id
T’T/♥FF♥(E)F♥id
F(E♥)EE♥+T
States 10,11,12
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
F(♥E)E♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
Fid♥
E’E+♥TT♥T/FT♥FF♥(E)F♥id
T’T/♥FF♥(E)F♥id
F(E♥)EE♥+T
E’E+T♥TT♥/F
T’T/F♥
F(E)♥
States 1,2,3,4,... 12
E’♥EE♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
E’E♥EE♥ + T
E’T♥TT♥ /F
TF♥
F(♥E)E♥E + TE♥TT♥T/FT♥FF♥(E)F♥id
Fid♥
E’E+♥TT♥T/FT♥FF♥(E)F♥id
T’T/♥FF♥(E)F♥id
F(E♥)EE♥+T
E’E+T♥TT♥/F
T’T/F♥
F(E)♥
END
Canonical Collection LR