/* Parser implementation */

/* For a description, see the comments at end of this file */

/* XXX To do: error recovery */

#include "Python.h"

#include "token.h"

#include "grammar.h"

#include "node.h"

#include "parser.h"

#include "errcode.h"

#include "graminit.h"

#ifdef Py_DEBUG

extern int Py_DebugFlag;

#define D(x) if (!Py_DebugFlag); else x

#else

#define D(x)

#endif

/* STACK DATA TYPE */

static void s_reset(stack *);

static void

s_reset(stack *s)

{

    s->s_top = &s->s_base[MAXSTACK];

}

#define s_empty(s) ((s)->s_top == &(s)->s_base[MAXSTACK])

static int

s_push(stack *s, const dfa *d, node *parent)

{

    stackentry *top;

    if (s->s_top == s->s_base) {

        fprintf(stderr, "s_push: parser stack overflow\n");

        return E_NOMEM;

    }

    top = --s->s_top;

    top->s_dfa = d;

    top->s_parent = parent;

    top->s_state = 0;

    return 0;

}

#ifdef Py_DEBUG

static void

s_pop(stack *s)

{

    if (s_empty(s))

        Py_FatalError("s_pop: parser stack underflow -- FATAL");

    s->s_top++;

}

#else /* !Py_DEBUG */

#define s_pop(s) (s)->s_top++

#endif

/* PARSER CREATION */

parser_state *

PyParser_New(grammar *g, int start)

{

    parser_state *ps;

    if (!g->g_accel)

        PyGrammar_AddAccelerators(g);

    ps = (parser_state *)PyMem_MALLOC(sizeof(parser_state));

    if (ps == NULL)

        return NULL;

    ps->p_grammar = g;

#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD

    ps->p_flags = 0;

#endif

    ps->p_tree = PyNode_New(start);

    if (ps->p_tree == NULL) {

        PyMem_FREE(ps);

        return NULL;

    }

    s_reset(&ps->p_stack);

    (void) s_push(&ps->p_stack, PyGrammar_FindDFA(g, start), ps->p_tree);

    return ps;

}

void

PyParser_Delete(parser_state *ps)

{

    /* NB If you want to save the parse tree,

       you must set p_tree to NULL before calling delparser! */

    PyNode_Free(ps->p_tree);

    PyMem_FREE(ps);

}

/* PARSER STACK OPERATIONS */

static int

shift(stack *s, int type, char *str, int newstate, int lineno, int col_offset,

      int end_lineno, int end_col_offset)

{

    int err;

    assert(!s_empty(s));

    err = PyNode_AddChild(s->s_top->s_parent, type, str, lineno, col_offset,

                          end_lineno, end_col_offset);

    if (err)

        return err;

    s->s_top->s_state = newstate;

    return 0;

}

static int

push(stack *s, int type, const dfa *d, int newstate, int lineno, int col_offset,

     int end_lineno, int end_col_offset)

{

    int err;

    node *n;

    n = s->s_top->s_parent;

    assert(!s_empty(s));

    err = PyNode_AddChild(n, type, (char *)NULL, lineno, col_offset,

                          end_lineno, end_col_offset);

    if (err)

        return err;

    s->s_top->s_state = newstate;

    return s_push(s, d, CHILD(n, NCH(n)-1));

}

/* PARSER PROPER */

static int

classify(parser_state *ps, int type, const char *str)

{

    grammar *g = ps->p_grammar;

    int n = g->g_ll.ll_nlabels;

    if (type == NAME) {

        const label *l = g->g_ll.ll_label;

        int i;

        for (i = n; i > 0; i--, l++) {

            if (l->lb_type != NAME || l->lb_str == NULL ||

                l->lb_str[0] != str[0] ||

                strcmp(l->lb_str, str) != 0)

                continue;

#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD

#if 0

            /* Leaving this in as an example */

            if (!(ps->p_flags & CO_FUTURE_WITH_STATEMENT)) {

                if (str[0] == 'w' && strcmp(str, "with") == 0)

                    break; /* not a keyword yet */

                else if (str[0] == 'a' && strcmp(str, "as") == 0)

                    break; /* not a keyword yet */

            }

#endif

#endif

            D(printf("It's a keyword\n"));

            return n - i;

        }

    }

    {

        const label *l = g->g_ll.ll_label;

        int i;

        for (i = n; i > 0; i--, l++) {

            if (l->lb_type == type && l->lb_str == NULL) {

                D(printf("It's a token we know\n"));

                return n - i;

            }

        }

    }

    D(printf("Illegal token\n"));

    return -1;

}

#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD

#if 0

/* Leaving this in as an example */

static void

future_hack(parser_state *ps)

{

    node *n = ps->p_stack.s_top->s_parent;

    node *ch, *cch;

    int i;

    /* from __future__ import ..., must have at least 4 children */

    n = CHILD(n, 0);

    if (NCH(n) < 4)

        return;

    ch = CHILD(n, 0);

    if (STR(ch) == NULL || strcmp(STR(ch), "from") != 0)

        return;

    ch = CHILD(n, 1);

    if (NCH(ch) == 1 && STR(CHILD(ch, 0)) &&

        strcmp(STR(CHILD(ch, 0)), "__future__") != 0)

        return;

    ch = CHILD(n, 3);

    /* ch can be a star, a parenthesis or import_as_names */

    if (TYPE(ch) == STAR)

        return;

    if (TYPE(ch) == LPAR)

        ch = CHILD(n, 4);

    for (i = 0; i < NCH(ch); i += 2) {

        cch = CHILD(ch, i);

        if (NCH(cch) >= 1 && TYPE(CHILD(cch, 0)) == NAME) {

            char *str_ch = STR(CHILD(cch, 0));

            if (strcmp(str_ch, FUTURE_WITH_STATEMENT) == 0) {

                ps->p_flags |= CO_FUTURE_WITH_STATEMENT;

            } else if (strcmp(str_ch, FUTURE_PRINT_FUNCTION) == 0) {

                ps->p_flags |= CO_FUTURE_PRINT_FUNCTION;

            } else if (strcmp(str_ch, FUTURE_UNICODE_LITERALS) == 0) {

                ps->p_flags |= CO_FUTURE_UNICODE_LITERALS;

            }

        }

    }

}

#endif

#endif /* future keyword */

int

PyParser_AddToken(parser_state *ps, int type, char *str,

                  int lineno, int col_offset,

                  int end_lineno, int end_col_offset,

                  int *expected_ret)

{

    int ilabel;

    int err;

    D(printf("Token %s/'%s' ... ", _PyParser_TokenNames[type], str));

    /* Find out which label this token is */

    ilabel = classify(ps, type, str);

    if (ilabel < 0)

        return E_SYNTAX;

    /* Loop until the token is shifted or an error occurred */

    for (;;) {

        /* Fetch the current dfa and state */

        const dfa *d = ps->p_stack.s_top->s_dfa;

        state *s = &d->d_state[ps->p_stack.s_top->s_state];

        D(printf(" DFA '%s', state %d:",

            d->d_name, ps->p_stack.s_top->s_state));

        /* Check accelerator */

        if (s->s_lower <= ilabel && ilabel < s->s_upper) {

            int x = s->s_accel[ilabel - s->s_lower];

            if (x != -1) {

                if (x & (1<<7)) {

                    /* Push non-terminal */

                    int nt = (x >> 8) + NT_OFFSET;

                    int arrow = x & ((1<<7)-1);

                    if (nt == func_body_suite && !(ps->p_flags & PyCF_TYPE_COMMENTS)) {

                        /* When parsing type comments is not requested,

                           we can provide better errors about bad indentation

                           by using 'suite' for the body of a funcdef */

                        D(printf(" [switch func_body_suite to suite]"));

                        nt = suite;

                    }

                    const dfa *d1 = PyGrammar_FindDFA(

                        ps->p_grammar, nt);

                    if ((err = push(&ps->p_stack, nt, d1,

                        arrow, lineno, col_offset,

                        end_lineno, end_col_offset)) > 0) {

                        D(printf(" MemError: push\n"));

                        return err;

                    }

                    D(printf(" Push '%s'\n", d1->d_name));

                    continue;

                }

                /* Shift the token */

                if ((err = shift(&ps->p_stack, type, str,

                                x, lineno, col_offset,

                                end_lineno, end_col_offset)) > 0) {

                    D(printf(" MemError: shift.\n"));

                    return err;

                }

                D(printf(" Shift.\n"));

                /* Pop while we are in an accept-only state */

                while (s = &d->d_state

                                [ps->p_stack.s_top->s_state],

                    s->s_accept && s->s_narcs == 1) {

                    D(printf("  DFA '%s', state %d: "

                             "Direct pop.\n",

                             d->d_name,

                             ps->p_stack.s_top->s_state));

#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD

#if 0

                    if (d->d_name[0] == 'i' &&

                        strcmp(d->d_name,

                           "import_stmt") == 0)

                        future_hack(ps);

#endif

#endif

                    s_pop(&ps->p_stack);

                    if (s_empty(&ps->p_stack)) {

                        D(printf("  ACCEPT.\n"));

                        return E_DONE;

                    }

                    d = ps->p_stack.s_top->s_dfa;

                }

                return E_OK;

            }

        }

        if (s->s_accept) {

#ifdef PY_PARSER_REQUIRES_FUTURE_KEYWORD

#if 0

            if (d->d_name[0] == 'i' &&

                strcmp(d->d_name, "import_stmt") == 0)

                future_hack(ps);

#endif

#endif

            /* Pop this dfa and try again */

            s_pop(&ps->p_stack);

            D(printf(" Pop ...\n"));

            if (s_empty(&ps->p_stack)) {

                D(printf(" Error: bottom of stack.\n"));

                return E_SYNTAX;

            }

            continue;

        }

        /* Stuck, report syntax error */

        D(printf(" Error.\n"));

        if (expected_ret) {

            if (s->s_lower == s->s_upper - 1) {

                /* Only one possible expected token */

                *expected_ret = ps->p_grammar->

                    g_ll.ll_label[s->s_lower].lb_type;

            }

            else

                *expected_ret = -1;

        }

        return E_SYNTAX;

    }

}

#ifdef Py_DEBUG

/* DEBUG OUTPUT */

void

dumptree(grammar *g, node *n)

{

    int i;

    if (n == NULL)

        printf("NIL");

    else {

        label l;

        l.lb_type = TYPE(n);

        l.lb_str = STR(n);

        printf("%s", PyGrammar_LabelRepr(&l));

        if (ISNONTERMINAL(TYPE(n))) {

            printf("(");

            for (i = 0; i < NCH(n); i++) {

                if (i > 0)

                    printf(",");

                dumptree(g, CHILD(n, i));

            }

            printf(")");

        }

    }

}

void

showtree(grammar *g, node *n)

{

    int i;

    if (n == NULL)

        return;

    if (ISNONTERMINAL(TYPE(n))) {

        for (i = 0; i < NCH(n); i++)

            showtree(g, CHILD(n, i));

    }

    else if (ISTERMINAL(TYPE(n))) {

        printf("%s", _PyParser_TokenNames[TYPE(n)]);

        if (TYPE(n) == NUMBER || TYPE(n) == NAME)

            printf("(%s)", STR(n));

        printf(" ");

    }

    else

        printf("? ");

}

void

printtree(parser_state *ps)

{

    if (Py_DebugFlag) {

        printf("Parse tree:\n");

        dumptree(ps->p_grammar, ps->p_tree);

        printf("\n");

        printf("Tokens:\n");

        showtree(ps->p_grammar, ps->p_tree);

        printf("\n");

    }

    printf("Listing:\n");

    PyNode_ListTree(ps->p_tree);

    printf("\n");

}

#endif /* Py_DEBUG */

/*

Description

-----------

The parser's interface is different than usual: the function addtoken()

must be called for each token in the input.  This makes it possible to

turn it into an incremental parsing system later.  The parsing system

constructs a parse tree as it goes.

A parsing rule is represented as a Deterministic Finite-state Automaton

(DFA).  A node in a DFA represents a state of the parser; an arc represents

a transition.  Transitions are either labeled with terminal symbols or

with non-terminals.  When the parser decides to follow an arc labeled

with a non-terminal, it is invoked recursively with the DFA representing

the parsing rule for that as its initial state; when that DFA accepts,

the parser that invoked it continues.  The parse tree constructed by the

recursively called parser is inserted as a child in the current parse tree.

The DFA's can be constructed automatically from a more conventional

language description.  An extended LL(1) grammar (ELL(1)) is suitable.

Certain restrictions make the parser's life easier: rules that can produce

the empty string should be outlawed (there are other ways to put loops

or optional parts in the language).  To avoid the need to construct

FIRST sets, we can require that all but the last alternative of a rule

(really: arc going out of a DFA's state) must begin with a terminal

symbol.

As an example, consider this grammar:

expr:   term (OP term)*

term:   CONSTANT | '(' expr ')'

The DFA corresponding to the rule for expr is:

------->.---term-->.------->

    ^          |

    |          |

    \----OP----/

The parse tree generated for the input a+b is:

(expr: (term: (NAME: a)), (OP: +), (term: (NAME: b)))

*/