- finite state machine that parses the specified grammar.
- This information is generated by the function generate_states
- in the file LR0.
-
-Each state of the machine is described by a set of items --
-particular positions in particular rules -- that are the possible
-places where parsing could continue when the machine is in this state.
-These symbols at these items are the allowable inputs that can follow now.
-
-A core represents one state. States are numbered in the number field.
-When generate_states is finished, the starting state is state 0
-and nstates is the number of states. (A transition to a state
-whose state number is nstates indicates termination.) All the cores
-are chained together and first_state points to the first one (state 0).
-
-For each state there is a particular symbol which must have been the
-last thing accepted to reach that state. It is the accessing_symbol
-of the core.
-
-Each core contains a vector of nitems items which are the indices
-in the ritems vector of the items that are selected in this state.
-
-The link field is used for chaining buckets that hash states by
-their itemsets. This is for recognizing equivalent states and
-combining them when the states are generated.
-
-The two types of transitions are shifts (push the lookahead token
-and read another) and reductions (combine the last n things on the
-stack via a rule, replace them with the symbol that the rule derives,
-and leave the lookahead token alone). When the states are generated,
-these transitions are represented in two other lists.
-
-Each shifts structure describes the possible shift transitions out
-of one state, the state whose number is in the number field.
-The shifts structures are linked through next and first_shift points to them.
-Each contains a vector of numbers of the states that shift transitions
-can go to. The accessing_symbol fields of those states' cores say what kind
-of input leads to them.
-
-A shift to state zero should be ignored. Conflict resolution
-deletes shifts by changing them to zero.
-
-Each reductions structure describes the possible reductions at the state
-whose number is in the number field. The data is a list of nreds rules,
-represented by their rule numbers. first_reduction points to the list
-of these structures.
-
-Conflict resolution can decide that certain tokens in certain
-states should explicitly be errors (for implementing %nonassoc).
-For each state, the tokens that are errors for this reason
-are recorded in an errs structure, which has the state number
-in its number field. The rest of the errs structure is full
-of token numbers.
-
-There is at least one shift transition present in state zero.
-It leads to a next-to-final state whose accessing_symbol is
-the grammar's start symbol. The next-to-final state has one shift
-to the final state, whose accessing_symbol is zero (end of input).
-The final state has one shift, which goes to the termination state
-(whose number is nstates-1).
-The reason for the extra state at the end is to placate the parser's
-strategy of making all decisions one token ahead of its actions. */
-
-
-typedef
- struct core
- {
- struct core *next;
- struct core *link;
- short number;
- short accessing_symbol;
- short nitems;
- short items[1];
- }
- core;
-
-
-
-typedef
- struct shifts
- {
- struct shifts *next;
- short number;
- short nshifts;
- short shifts[1];
- }
- shifts;
-
-
-
-typedef
- struct errs
- {
- short nerrs;
- short errs[1];
- }
- errs;
-
-
-
-typedef
- struct reductions
- {
- struct reductions *next;
- short number;
- short nreds;
- short rules[1];
- }
- reductions;
-
-
+ finite state machine that parses the specified grammar. This
+ information is generated by the function generate_states in the
+ file LR0.
+
+ Each state of the machine is described by a set of items --
+ particular positions in particular rules -- that are the possible
+ places where parsing could continue when the machine is in this
+ state. These symbols at these items are the allowable inputs that
+ can follow now.
+
+ A core represents one state. States are numbered in the number
+ field. When generate_states is finished, the starting state is
+ state 0 and nstates is the number of states. (A transition to a
+ state whose state number is nstates indicates termination.) All
+ the cores are chained together and first_state points to the first
+ one (state 0).
+
+ For each state there is a particular symbol which must have been
+ the last thing accepted to reach that state. It is the
+ accessing_symbol of the core.
+
+ Each core contains a vector of nitems items which are the indices
+ in the ritems vector of the items that are selected in this state.
+
+ The link field is used for chaining buckets that hash states by
+ their itemsets. This is for recognizing equivalent states and
+ combining them when the states are generated.
+
+ The two types of transitions are shifts (push the lookahead token
+ and read another) and reductions (combine the last n things on the
+ stack via a rule, replace them with the symbol that the rule
+ derives, and leave the lookahead token alone). When the states are
+ generated, these transitions are represented in two other lists.
+
+ Each shifts structure describes the possible shift transitions out
+ of one state, the state whose number is in the number field. The
+ shifts structures are linked through next and first_shift points to
+ them. Each contains a vector of numbers of the states that shift
+ transitions can go to. The accessing_symbol fields of those
+ states' cores say what kind of input leads to them.
+
+ A shift to state zero should be ignored. Conflict resolution
+ deletes shifts by changing them to zero.
+
+ Each reductions structure describes the possible reductions at the
+ state whose number is in the number field. The data is a list of
+ nreds rules, represented by their rule numbers. first_reduction
+ points to the list of these structures.
+
+ Conflict resolution can decide that certain tokens in certain
+ states should explicitly be errors (for implementing %nonassoc).
+ For each state, the tokens that are errors for this reason are
+ recorded in an errs structure, which has the state number in its
+ number field. The rest of the errs structure is full of token
+ numbers.
+
+ There is at least one shift transition present in state zero. It
+ leads to a next-to-final state whose accessing_symbol is the
+ grammar's start symbol. The next-to-final state has one shift to
+ the final state, whose accessing_symbol is zero (end of input).
+ The final state has one shift, which goes to the termination state
+ (whose number is nstates-1). The reason for the extra state at the
+ end is to placate the parser's strategy of making all decisions one
+ token ahead of its actions. */
+
+#ifndef STATE_H_
+# define STATE_H_
+
+typedef struct core
+{
+ struct core *next;
+ struct core *link;
+ short number;
+ short accessing_symbol;
+ short nitems;
+ short items[1];
+}
+core;
+
+
+
+typedef struct shifts
+{
+ struct shifts *next;
+ short number;
+ short nshifts;
+ short shifts[1];
+}
+shifts;
+
+
+
+typedef struct errs
+{
+ short nerrs;
+ short errs[1];
+}
+errs;
+
+
+
+typedef struct reductions
+{
+ struct reductions *next;
+ short number;
+ short nreds;
+ short rules[1];
+}
+reductions;
projects / bison.git / commitdiff
