- 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;
-
-
-
-extern int nstates;
-extern core *first_state;
-extern shifts *first_shift;
-extern reductions *first_reduction;
+ 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. (FIXME: This sentence
+ is no longer true: 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 two types of actions are shifts/gotos (push the look-ahead token
+ and read another/goto to the state designated by a nterm) 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
+ look-ahead token alone). When the states are generated, these
+ actions are represented in two other lists.
+
+ Each transition structure describes the possible transitions out
+ of one state, the state whose number is in the number field. Each
+ contains a vector of numbers of the states that transitions can go
+ to. The accessing_symbol fields of those states' cores say what
+ kind of input leads to them.
+
+ A transition to state zero should be ignored: conflict resolution
+ deletes transitions by having them point 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 holds the token numbers.
+
+ There is at least one goto 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.
+ 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_
+
+# include <bitset.h>
+
+# include "gram.h"
+# include "symtab.h"
+
+
+/*-------------------.
+| Numbering states. |
+`-------------------*/
+
+typedef int state_number;
+# define STATE_NUMBER_MAXIMUM INT_MAX
+
+/* Be ready to map a state_number to an int. */
+static inline int
+state_number_as_int (state_number s)
+{
+ return s;
+}
+
+
+typedef struct state state;
+
+/*--------------.
+| Transitions. |
+`--------------*/
+
+typedef struct
+{
+ int num;
+ state *states[1];
+} transitions;
+
+
+/* What is the symbol labelling the transition to
+ TRANSITIONS->states[Num]? Can be a token (amongst which the error
+ token), or non terminals in case of gotos. */
+
+#define TRANSITION_SYMBOL(Transitions, Num) \
+ (Transitions->states[Num]->accessing_symbol)
+
+/* Is the TRANSITIONS->states[Num] a shift? (as opposed to gotos). */
+
+#define TRANSITION_IS_SHIFT(Transitions, Num) \
+ (ISTOKEN (TRANSITION_SYMBOL (Transitions, Num)))
+
+/* Is the TRANSITIONS->states[Num] a goto?. */
+
+#define TRANSITION_IS_GOTO(Transitions, Num) \
+ (!TRANSITION_IS_SHIFT (Transitions, Num))
+
+/* Is the TRANSITIONS->states[Num] labelled by the error token? */
+
+#define TRANSITION_IS_ERROR(Transitions, Num) \
+ (TRANSITION_SYMBOL (Transitions, Num) == errtoken->number)
+
+/* When resolving a SR conflicts, if the reduction wins, the shift is
+ disabled. */
+
+#define TRANSITION_DISABLE(Transitions, Num) \
+ (Transitions->states[Num] = NULL)
+
+#define TRANSITION_IS_DISABLED(Transitions, Num) \
+ (Transitions->states[Num] == NULL)
+
+
+/* Iterate over each transition over a token (shifts). */
+#define FOR_EACH_SHIFT(Transitions, Iter) \
+ for (Iter = 0; \
+ Iter < Transitions->num \
+ && (TRANSITION_IS_DISABLED (Transitions, Iter) \
+ || TRANSITION_IS_SHIFT (Transitions, Iter)); \
+ ++Iter) \
+ if (!TRANSITION_IS_DISABLED (Transitions, Iter))
+
+
+/* Return the state such SHIFTS contain a shift/goto to it on SYM.
+ Abort if none found. */
+struct state *transitions_to (transitions *shifts, symbol_number sym);
+
+
+/*-------.
+| Errs. |
+`-------*/
+
+typedef struct
+{
+ int num;
+ symbol *symbols[1];
+} errs;
+
+errs *errs_new (int num, symbol **tokens);
+
+
+/*-------------.
+| Reductions. |
+`-------------*/
+
+typedef struct
+{
+ int num;
+ bitset *look_ahead_tokens;
+ rule *rules[1];
+} reductions;
+
+
+
+/*---------.
+| states. |
+`---------*/
+
+struct state
+{
+ state_number number;
+ symbol_number accessing_symbol;
+ transitions *transitions;
+ reductions *reductions;
+ errs *errs;
+
+ /* Nonzero if no look-ahead is needed to decide what to do in state S. */
+ char consistent;
+
+ /* If some conflicts were solved thanks to precedence/associativity,
+ a human readable description of the resolution. */
+ const char *solved_conflicts;
+
+ /* Its items. Must be last, since ITEMS can be arbitrarily large.
+ */
+ size_t nitems;
+ item_number items[1];
+};
+
+extern state_number nstates;
+extern state *final_state;
+
+/* Create a new state with ACCESSING_SYMBOL for those items. */
+state *state_new (symbol_number accessing_symbol,
+ size_t core_size, item_number *core);
+
+/* Set the transitions of STATE. */
+void state_transitions_set (state *s, int num, state **trans);
+
+/* Set the reductions of STATE. */
+void state_reductions_set (state *s, int num, rule **reds);
+
+int state_reduction_find (state *s, rule *r);
+
+/* Set the errs of STATE. */
+void state_errs_set (state *s, int num, symbol **errors);
+
+/* Print on OUT all the look-ahead tokens such that this STATE wants to
+ reduce R. */
+void state_rule_look_ahead_tokens_print (state *s, rule *r, FILE *out);
+
+/* Create/destroy the states hash table. */
+void state_hash_new (void);
+void state_hash_free (void);
+
+/* Find the state associated to the CORE, and return it. If it does
+ not exist yet, return NULL. */
+state *state_hash_lookup (size_t core_size, item_number *core);
+
+/* Insert STATE in the state hash table. */
+void state_hash_insert (state *s);
+
+/* All the states, indexed by the state number. */
+extern state **states;
+
+/* Free all the states. */
+void states_free (void);
+#endif /* !STATE_H_ */
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