interpreter.c

/*********************************************************************

  Gazelle: a system for building fast, reusable parsers

  interpreter.c

  Once a compiled grammar has been loaded into memory, the routines
  in this file are what actually does the parsing.  This file is an
  "interpreter" in the sense that it parses the input by using the
  grammar as a data structure -- no grammar-specific code is ever
  generated or executed.  Despite this, it is still quite fast, and
  has a very low memory footprint.

  The interpreter primarily consists of maintaining the parse stack
  properly and transitioning the frames in response to the input.

  Copyright (c) 2007-2008 Joshua Haberman.  See LICENSE for details.

*********************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
#include "interpreter.h"

/*
 * A diagnostic function for dumping the current state of the stack.
 */
void dump_stack(struct parse_state *s, FILE *output)
{
    fprintf(output, "Stack dump:\n");
    struct grammar *g = s->bound_grammar->grammar;
    for(int i = 0; i < s->parse_stack_len; i++)
    {
        struct parse_stack_frame *frame = &s->parse_stack[i];
        switch(frame->frame_type)
        {
            case FRAME_TYPE_RTN:
            {
                struct rtn_frame *rtn_frame = &frame->f.rtn_frame;
                fprintf(output, "RTN: %s", rtn_frame->rtn->name);
                break;
            }

            case FRAME_TYPE_GLA:
            {
                struct gla_frame *gla_frame = &frame->f.gla_frame;
                fprintf(output, "GLA: #%d", gla_frame->gla - g->glas);
                break;
            }

            case FRAME_TYPE_INTFA:
            {
                struct intfa_frame *intfa_frame = &frame->f.intfa_frame;
                fprintf(output, "IntFA: #%d", intfa_frame->intfa - g->intfas);
                break;
            }
        }
        fprintf(output, ", start_offset: %d, eof_ok: %d\n", frame->start_offset, frame->eof_ok);
    }
    fprintf(output, "\n");
}

struct parse_stack_frame *push_empty_frame(struct parse_state *s, enum frame_type frame_type,
                                           int start_offset)
{
    RESIZE_DYNARRAY(s->parse_stack, s->parse_stack_len+1);
    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    frame->frame_type = frame_type;
    frame->start_offset = start_offset;
    return frame;
}

struct intfa_frame *push_intfa_frame(struct parse_state *s, struct intfa *intfa, int start_offset)
{
    struct parse_stack_frame *old_frame = DYNARRAY_GET_TOP(s->parse_stack);
    struct parse_stack_frame *frame = push_empty_frame(s, FRAME_TYPE_INTFA, start_offset);
    struct intfa_frame *intfa_frame = &frame->f.intfa_frame;
    intfa_frame->intfa        = intfa;
    intfa_frame->intfa_state  = &intfa->states[0];

    /* IntFA frames start out being eof_ok if the parent frame is, but become not ok
     * when they transition out of the initial state. */
    frame->eof_ok       = old_frame->eof_ok;

    return intfa_frame;
}

struct parse_stack_frame *push_gla_frame(struct parse_state *s, struct gla *gla, int start_offset)
{
    struct parse_stack_frame *old_frame = DYNARRAY_GET_TOP(s->parse_stack);
    struct parse_stack_frame *frame = push_empty_frame(s, FRAME_TYPE_GLA, start_offset);
    struct gla_frame *gla_frame = &frame->f.gla_frame;
    gla_frame->gla          = gla;
    gla_frame->gla_state    = &gla->states[0];

    /* GLA frames start out being eof_ok if the parent frame is, but become not ok
     * when they transition out of the initial state. */
    frame->eof_ok       = old_frame->eof_ok;

    return frame;
}

struct parse_stack_frame *push_rtn_frame(struct parse_state *s, struct rtn *rtn, int start_offset)
{
    struct parse_stack_frame *old_frame = DYNARRAY_GET_TOP(s->parse_stack);
    struct parse_stack_frame *new_frame = push_empty_frame(s, FRAME_TYPE_RTN, start_offset);
    struct rtn_frame *new_rtn_frame = &new_frame->f.rtn_frame;

    new_rtn_frame->rtn            = rtn;
    new_rtn_frame->rtn_transition = NULL;
    new_rtn_frame->rtn_state      = &new_rtn_frame->rtn->states[0];

    /* RTN frames start out being eof_ok iff their start state is a final state
     * *and* their parent is eof_ok. */
    new_frame->eof_ok             = old_frame->eof_ok && rtn->states[0].is_final;

    /* Call start rule callback if set */
    if(s->bound_grammar->start_rule_cb)
    {
        s->bound_grammar->start_rule_cb(s);
    }

    return new_frame;
}

struct parse_stack_frame *push_rtn_frame_for_transition(struct parse_state *s,
                                                        struct rtn_transition *t,
                                                        int start_offset)
{
    struct rtn_frame *old_rtn_frame = &DYNARRAY_GET_TOP(s->parse_stack)->f.rtn_frame;
    old_rtn_frame->rtn_transition = t;
    return push_rtn_frame(s, t->edge.nonterminal, start_offset);
}

struct parse_stack_frame *pop_frame(struct parse_state *s)
{
    assert(s->parse_stack_len > 0);
    RESIZE_DYNARRAY(s->parse_stack, s->parse_stack_len-1);

    struct parse_stack_frame *frame;
    if(s->parse_stack_len > 0)
        frame = DYNARRAY_GET_TOP(s->parse_stack);
    else
        frame = NULL;

    return frame;
}

void set_eof_ok_flag_for_rtn_frame(struct parse_state *s)
{
    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    assert(frame->frame_type == FRAME_TYPE_RTN);
    struct rtn_frame *rtn_frame = &frame->f.rtn_frame;
    if(rtn_frame->rtn_state->is_final &&
       (s->parse_stack_len == 0 || s->parse_stack[s->parse_stack_len-2].eof_ok))
        frame->eof_ok = true;
    else
        frame->eof_ok = false;
}

struct parse_stack_frame *pop_rtn_frame(struct parse_state *s)
{
    assert(DYNARRAY_GET_TOP(s->parse_stack)->frame_type == FRAME_TYPE_RTN);

    /* Call end rule callback if set */
    if(s->bound_grammar->end_rule_cb)
    {
        s->bound_grammar->end_rule_cb(s);
    }

    struct parse_stack_frame *frame = pop_frame(s);
    if(frame != NULL)
    {
        struct rtn_frame *rtn_frame = &frame->f.rtn_frame;
        if(rtn_frame->rtn_transition)
        {
            rtn_frame->rtn_state = rtn_frame->rtn_transition->dest_state;
            set_eof_ok_flag_for_rtn_frame(s);
        }
    }
    return frame;
}

struct parse_stack_frame *pop_gla_frame(struct parse_state *s)
{
    assert(DYNARRAY_GET_TOP(s->parse_stack)->frame_type == FRAME_TYPE_GLA);
    return pop_frame(s);
}

struct parse_stack_frame *pop_intfa_frame(struct parse_state *s)
{
    assert(DYNARRAY_GET_TOP(s->parse_stack)->frame_type == FRAME_TYPE_INTFA);
    return pop_frame(s);
}

/*
 * descend_to_gla(): given the current parse stack, pushes any RTN or GLA
 * stack frames representing transitions that can be taken without consuming
 * any terminals.
 *
 * Preconditions:
 * - the current frame is either an RTN frame or a GLA frame
 *
 * Postconditions:
 * - the current frame is an RTN frame or a GLA frame.  If a new GLA frame was
 *   entered, entered_gla is set to true.
 */
struct parse_stack_frame *descend_to_gla(struct parse_state *s, bool *entered_gla, int start_offset)
{
    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    *entered_gla = false;

    while(frame->frame_type == FRAME_TYPE_RTN)
    {
        struct rtn_frame *rtn_frame = &frame->f.rtn_frame;
        switch(rtn_frame->rtn_state->lookahead_type)
        {
          case STATE_HAS_INTFA:
            return frame;
            break;

          case STATE_HAS_GLA:
            *entered_gla = true;
            return push_gla_frame(s, rtn_frame->rtn_state->d.state_gla, start_offset);
            break;

          case STATE_HAS_NEITHER:
            /* An RTN state has neither an IntFA or a GLA in only two cases:
             * - it is a final state with no outgoing transitions
             * - it is a nonfinal state with only one transition (a nonterminal) */
            assert(rtn_frame->rtn_state->num_transitions < 2);
            if(rtn_frame->rtn_state->num_transitions == 0)
            {
                /* Final state */
                frame = pop_rtn_frame(s);
                if(frame == NULL) return NULL;
            }
            else if(rtn_frame->rtn_state->num_transitions == 1)
            {
                assert(rtn_frame->rtn_state->transitions[0].transition_type == NONTERM_TRANSITION);
                frame = push_rtn_frame_for_transition(s, &rtn_frame->rtn_state->transitions[0],
                                                      start_offset);
            }
            break;
        }
    }
    return frame;
}

struct intfa_frame *push_intfa_frame_for_gla_or_rtn(struct parse_state *s, int start_offset)
{
    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    if(frame->frame_type == FRAME_TYPE_GLA)
    {
        assert(frame->f.gla_frame.gla_state->is_final == false);
        return push_intfa_frame(s, frame->f.gla_frame.gla_state->d.nonfinal.intfa, start_offset);
    }
    else if(frame->frame_type == FRAME_TYPE_RTN)
    {
        return push_intfa_frame(s, frame->f.rtn_frame.rtn_state->d.state_intfa, start_offset);
    }
    assert(false);
    return NULL;
}

struct parse_stack_frame *do_rtn_terminal_transition(struct parse_state *s,
                                                     struct rtn_transition *t,
                                                     struct terminal *terminal)
{
    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    assert(frame->frame_type == FRAME_TYPE_RTN);
    struct rtn_frame *rtn_frame = &frame->f.rtn_frame;

    /* Call terminal callback if set */
    if(s->bound_grammar->terminal_cb)
    {
        rtn_frame->rtn_transition = t;
        s->bound_grammar->terminal_cb(s, terminal);
    }

    assert(t->transition_type == TERMINAL_TRANSITION);
    rtn_frame->rtn_state = t->dest_state;
    set_eof_ok_flag_for_rtn_frame(s);
    return frame;
}

struct rtn_transition *find_rtn_terminal_transition(struct parse_state *s,
                                                    struct terminal *terminal)
{
    struct parse_stack_frame *frame = &s->parse_stack[s->parse_stack_len-1];
    struct rtn_frame *rtn_frame = &frame->f.rtn_frame;
    for(int i = 0; i < rtn_frame->rtn_state->num_transitions; i++)
    {
        struct rtn_transition *t = &rtn_frame->rtn_state->transitions[i];
        if(t->transition_type == TERMINAL_TRANSITION && t->edge.terminal_name == terminal->name)
        {
            return t;
        }
    }

    return NULL;
}

/*
 * do_gla_transition(): transitions a GLA frame, performing the appropriate
 * RTN transitions if this puts the GLA in a final state.
 *
 * Preconditions:
 * - the current stack frame is a GLA frame
 * - term is a terminal that came from this GLA state's intfa
 *
 * Postconditions:
 * - the current stack frame is a GLA frame (this would indicate that
 *   the GLA hasn't hit a final state yet) or the current stack frame is
 *   an RTN frame (indicating we *have* hit a final state in the GLA)
 */
struct parse_stack_frame *do_gla_transition(struct parse_state *s,
                                            struct terminal *gla_term,
                                            int *rtn_term_offset)
{
    struct parse_stack_frame *frame = &s->parse_stack[s->parse_stack_len-1];
    assert(frame->frame_type == FRAME_TYPE_GLA);
    assert(frame->f.gla_frame.gla_state->is_final == false);
    struct gla_state *gla_state = frame->f.gla_frame.gla_state;
    struct gla_state *dest_gla_state = NULL;

    for(int i = 0; i < gla_state->d.nonfinal.num_transitions; i++)
    {
        struct gla_transition *t = &gla_state->d.nonfinal.transitions[i];
        if(t->term == gla_term->name)
        {
            frame->f.gla_frame.gla_state = dest_gla_state = t->dest_state;
        }
    }
    assert(dest_gla_state);

    if(dest_gla_state->is_final)
    {
        /* pop the GLA frame (since now we know what RTN transition to take)
         * and use its information to make an RTN transition */
        int offset = dest_gla_state->d.final.transition_offset;
        frame = pop_gla_frame(s);
        if(offset == 0)
        {
            frame = pop_rtn_frame(s);
        }
        else
        {
            struct rtn_transition *t = &frame->f.rtn_frame.rtn_state->transitions[offset-1];
            struct terminal *next_term = &s->token_buffer[*rtn_term_offset];
            if(t->transition_type == TERMINAL_TRANSITION)
            {
                /* The transition must match what we have in the token buffer */
                (*rtn_term_offset)++;
                assert(next_term->name == t->edge.terminal_name);
                frame = do_rtn_terminal_transition(s, t, next_term);
            }
            else
            {
                frame = push_rtn_frame_for_transition(s, t, next_term->offset+next_term->len);
            }
        }
    }
    return frame;
}

/*
 * process_terminal(): processes a terminal that was just lexed, possibly
 * triggering a series of RTN and/or GLA transitions.
 *
 * Preconditions:
 * - the current stack frame is an intfa frame representing the intfa that
 *   just produced this terminal
 * - the given terminal can be recognized by the current GLA or RTN state
 *
 * Postconditions:
 * - the current stack frame is an intfa frame representing the state after
 *   all available GLA and RTN transitions have been taken.
 */

struct intfa_frame *process_terminal(struct parse_state *s,
                                     char *term_name,
                                     int start_offset,
                                     int len)
{
    pop_intfa_frame(s);

    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    int rtn_term_offset = 0;
    int gla_term_offset = s->token_buffer_len;

    RESIZE_DYNARRAY(s->token_buffer, s->token_buffer_len+1);
    struct terminal *term = DYNARRAY_GET_TOP(s->token_buffer);
    term->name = term_name;
    term->offset = start_offset;
    term->len = len;

    /* Feed tokens to RTNs and GLAs until we have processed all the tokens we have */
    while(frame != NULL &&
          ((frame->frame_type == FRAME_TYPE_RTN && rtn_term_offset < s->token_buffer_len) ||
          (frame->frame_type == FRAME_TYPE_GLA && gla_term_offset < s->token_buffer_len)))
    {
        struct terminal *rtn_term = &s->token_buffer[rtn_term_offset];
        if(frame->frame_type == FRAME_TYPE_RTN)
        {
            struct rtn_transition *t;
            rtn_term_offset++;
            t = find_rtn_terminal_transition(s, rtn_term);
            if(!t)
            {
                fprintf(stderr, "Parse error: unexpected terminal %s at offset %d\n",
                        rtn_term->name, rtn_term->offset);
                exit(1);
            }

            frame = do_rtn_terminal_transition(s, t, rtn_term);
        }
        else
        {
            struct terminal *gla_term = &s->token_buffer[gla_term_offset++];
            frame = do_gla_transition(s, gla_term, &rtn_term_offset);
        }
        bool entered_gla;
        frame = descend_to_gla(s, &entered_gla, rtn_term->offset+rtn_term->len);
        if(entered_gla)
        {
            gla_term_offset = rtn_term_offset;
        }
    }

    /* Remove consumed terminals from token_buffer */
    int remaining_terminals = s->token_buffer_len - rtn_term_offset;

    if(frame == NULL)
    {
        /* EOF (as far as the parser is concerned */
        assert(remaining_terminals == 0);
        return NULL;
    }

    if(remaining_terminals > 0)
    {
        memmove(s->token_buffer, s->token_buffer + rtn_term_offset,
                remaining_terminals * sizeof(*s->token_buffer));
    }
    RESIZE_DYNARRAY(s->token_buffer, remaining_terminals);

    /* Now that we have processed all terminals that we currently can, push
     * an intfa frame to handle the next bytes */
    return push_intfa_frame_for_gla_or_rtn(s, start_offset+len);
}

/*
 * find_intfa_transition(): get the transition (if any) out of this state
 * on this character.
 */
struct intfa_transition *find_intfa_transition(struct intfa_frame *frame, char ch)
{
    for(int i = 0; i < frame->intfa_state->num_transitions; i++)
    {
        struct intfa_transition *t = &frame->intfa_state->transitions[i];
        if(ch >= t->ch_low && ch <= t->ch_high)
        {
            return t;
        }
    }

    return NULL;
}

/*
 * do_intfa_transition(): transitions an IntFA frame according to the given
 * char, performing the appropriate GLA/RTN transitions if this puts the IntFA
 * in a final state.
 *
 * Preconditions:
 * - the current stack frame is an IntFA frame
 *
 * Postconditions:
 * - the current stack frame is an IntFA frame unless we have hit a
 *   hard EOF in which case it is an RTN frame.  Note that it could be either
 *   same IntFA frame or a different one.
 *
 * Note: we currently implement longest-match, assuming that the first
 * non-matching character is only one longer than the longest match.
 */
struct intfa_frame *do_intfa_transition(struct parse_state *s,
                                        struct intfa_frame *intfa_frame,
                                        char ch)
{
    struct intfa_transition *t = find_intfa_transition(intfa_frame, ch);
    struct parse_stack_frame *frame = GET_PARSE_STACK_FRAME(intfa_frame);

    /* If this character did not have any transition, but the state we're coming
     * from is final, then longest-match semantics say that we should return
     * the last character's final state as the token.  But if the state we're
     * coming from is *not* final, it's just a parse error. */
    if(!t)
    {
        char *terminal = intfa_frame->intfa_state->final;
        assert(terminal);
        intfa_frame = process_terminal(s, terminal, frame->start_offset,
                                       s->offset - frame->start_offset);
        assert(intfa_frame);  // if this fails, it means that we hit a hard EOF

        /* This must succeed this time or it is a parse error */
        t = find_intfa_transition(intfa_frame, ch);
        assert(t);
    }

    /* We increment the offset here because we have just crossed the threshold
     * where we have finished processing all terminals for the previous byte and
     * started processing transitions for the current byte. */
    s->offset++;
    intfa_frame->intfa_state = t->dest_state;
    frame->eof_ok = false;

    /* If the current state is final and there are no outgoing transitions,
     * we *know* we don't have to wait any longer for the longest match.
     * Transition the RTN or GLA now, for more on-line behavior. */
    if(intfa_frame->intfa_state->final && (intfa_frame->intfa_state->num_transitions == 0))
    {
        intfa_frame = process_terminal(s, intfa_frame->intfa_state->final,
                                       frame->start_offset,
                                       s->offset - frame->start_offset);
    }

    return intfa_frame;
}

enum parse_status parse(struct parse_state *s, char *buf, int buf_len,
                        int *out_consumed_buf_len, bool *out_eof_ok)
{
    struct intfa_frame *intfa_frame;

    /* For the first parse, we need to descend from the starting frame
     * until we hit an IntFA frame. */
    if(s->offset == 0)
    {
        bool entered_gla;
        descend_to_gla(s, &entered_gla, 0);
        intfa_frame = push_intfa_frame_for_gla_or_rtn(s, 0);
    }
    else
    {
        struct parse_stack_frame *frame = &s->parse_stack[s->parse_stack_len-1];
        assert(frame->frame_type == FRAME_TYPE_INTFA);
        intfa_frame = &frame->f.intfa_frame;
    }

    for(int i = 0; i < buf_len; i++)
    {
        intfa_frame = do_intfa_transition(s, intfa_frame, buf[i]);
        if(intfa_frame == NULL)
        {
            if(out_consumed_buf_len) *out_consumed_buf_len = i+1;
            if(out_eof_ok) *out_eof_ok = true;
            assert(s->parse_stack_len == 0);
            return PARSE_STATUS_EOF;
        }
    }

    if(out_eof_ok) *out_eof_ok = DYNARRAY_GET_TOP(s->parse_stack)->eof_ok;
    if(out_consumed_buf_len) *out_consumed_buf_len = buf_len;

    return PARSE_STATUS_OK;
}

void finish_parse(struct parse_state *s)
{
    struct parse_stack_frame *frame = DYNARRAY_GET_TOP(s->parse_stack);
    while(s->parse_stack_len > 0)
    {
        assert(frame->eof_ok);
        if(frame->frame_type == FRAME_TYPE_RTN)
            frame = pop_rtn_frame(s);
        else
            frame = pop_frame(s);
    }
}

void reinit_parse_state(struct parse_state *s, struct bound_grammar *bg)
{
    s->offset = 0;
    s->bound_grammar = bg;
    RESIZE_DYNARRAY(s->parse_stack, 0);
    RESIZE_DYNARRAY(s->token_buffer, 0);
    push_rtn_frame(s, &bg->grammar->rtns[0], 0);
}

void free_parse_state(struct parse_state *s)
{
    FREE_DYNARRAY(s->parse_stack);
    FREE_DYNARRAY(s->token_buffer);
}

void init_parse_state(struct parse_state *s, struct bound_grammar *bg)
{
    s->offset = 0;
    s->bound_grammar = bg;
    INIT_DYNARRAY(s->parse_stack, 0, 16);
    INIT_DYNARRAY(s->token_buffer, 0, 2);
    push_rtn_frame(s, &bg->grammar->rtns[0], 0);
}


/*
 * Local Variables:
 * c-file-style: "bsd"
 * c-basic-offset: 4
 * indent-tabs-mode: nil
 * End:
 * vim:et:sts=4:sw=4
 */