luatexdir/tex/conditional.w

% conditional.w
%
% Copyright 2009-2010 Taco Hoekwater <taco@@luatex.org>
%
% This file is part of LuaTeX.
%
% LuaTeX is free software; you can redistribute it and/or modify it under
% the terms of the GNU General Public License as published by the Free
% Software Foundation; either version 2 of the License, or (at your
% option) any later version.
%
% LuaTeX is distributed in the hope that it will be useful, but WITHOUT
% ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
% FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
% License for more details.
%
% You should have received a copy of the GNU General Public License along
% with LuaTeX; if not, see <http://www.gnu.org/licenses/>.

@ @c


#include "ptexlib.h"

@ @c
#define box(A) eqtb[box_base+(A)].hh.rh

@* We consider now the way \TeX\ handles various kinds of \.{\\if} commands.

@ Conditions can be inside conditions, and this nesting has a stack
that is independent of the |save_stack|.

Four global variables represent the top of the condition stack:
|cond_ptr| points to pushed-down entries, if any; |if_limit| specifies
the largest code of a |fi_or_else| command that is syntactically legal;
|cur_if| is the name of the current type of conditional; and |if_line|
is the line number at which it began.

If no conditions are currently in progress, the condition stack has the
special state |cond_ptr=null|, |if_limit=normal|, |cur_if=0|, |if_line=0|.
Otherwise |cond_ptr| points to a two-word node; the |type|, |subtype|, and
|link| fields of the first word contain |if_limit|, |cur_if|, and
|cond_ptr| at the next level, and the second word contains the
corresponding |if_line|.

@c
halfword cond_ptr;              /* top of the condition stack */
int if_limit;                   /* upper bound on |fi_or_else| codes */
int cur_if;                     /* type of conditional being worked on */
int if_line;                    /* line where that conditional began */


@ When we skip conditional text, we keep track of the line number
where skipping began, for use in error messages.

@c
int skip_line;                  /* skipping began here */


@ Here is a procedure that ignores text until coming to an \.{\\or},
\.{\\else}, or \.{\\fi} at level zero of $\.{\\if}\ldots\.{\\fi}$
nesting. After it has acted, |cur_chr| will indicate the token that
was found, but |cur_tok| will not be set (because this makes the
procedure run faster).

@c
void pass_text(void)
{
    int l;                      /* level of $\.{\\if}\ldots\.{\\fi}$ nesting */
    int save_scanner_status;    /* |scanner_status| upon entry */
    save_scanner_status = scanner_status;
    scanner_status = skipping;
    l = 0;
    skip_line = line;
    while (1) {
        get_token_lua();
        if (cur_cmd == fi_or_else_cmd) {
            if (l == 0)
                break;
            if (cur_chr == fi_code)
                decr(l);
        } else if (cur_cmd == if_test_cmd) {
            incr(l);
        }
    }
    scanner_status = save_scanner_status;
    if (int_par(tracing_ifs_code) > 0)
        show_cur_cmd_chr();
}


@ When we begin to process a new \.{\\if}, we set |if_limit:=if_code|; then
if\/ \.{\\or} or \.{\\else} or \.{\\fi} occurs before the current \.{\\if}
condition has been evaluated, \.{\\relax} will be inserted.
For example, a sequence of commands like `\.{\\ifvoid1\\else...\\fi}'
would otherwise require something after the `\.1'.

@c
void push_condition_stack(void)
{
    halfword p = new_node(if_node, 0);
    vlink(p) = cond_ptr;
    if_limit_type(p) = (quarterword) if_limit;
    if_limit_subtype(p) = (quarterword) cur_if;
    if_line_field(p) = if_line;
    cond_ptr = p;
    cur_if = cur_chr;
    if_limit = if_code;
    if_line = line;
}

void pop_condition_stack(void)
{
    halfword p;
    if (if_stack[in_open] == cond_ptr)
        if_warning();
    /* conditionals possibly not properly nested with files */
    p = cond_ptr;
    if_line = if_line_field(p);
    cur_if = if_limit_subtype(p);
    if_limit = if_limit_type(p);
    cond_ptr = vlink(p);
    flush_node(p);
}


@ Here's a procedure that changes the |if_limit| code corresponding to
a given value of |cond_ptr|.

@c
void change_if_limit(int l, halfword p)
{
    halfword q;
    if (p == cond_ptr) {
        if_limit = l;           /* that's the easy case */
    } else {
        q = cond_ptr;
        while (1) {
            if (q == null)
                confusion("if");
            if (vlink(q) == p) {
                if_limit_type(q) = (quarterword) l;
                return;
            }
            q = vlink(q);
        }
    }
}


@ The conditional \.{\\ifcsname} is equivalent to \.{\\expandafter}
\.{\\expandafter} \.{\\ifdefined} \.{\\csname}, except that no new
control sequence will be entered into the hash table (once all tokens
preceding the mandatory \.{\\endcsname} have been expanded).

@c
static boolean test_for_cs(void)
{
    boolean b;                  /*is the condition true? */
    int m, s;                   /*to be tested against the second operand */
    halfword n, p, q;           /*for traversing token lists in \.{\\ifx} tests */
    n = get_avail();
    p = n;                      /*head of the list of characters */
    b = false;
    while (1) {
        get_x_token();
        if (cur_cs != 0)
            break;
        store_new_token(cur_tok);
    }
    if (cur_cmd != end_cs_name_cmd) {
        if (int_par(suppress_ifcsname_error_code)) {
            do {
                get_x_token();
            } while (cur_cmd != end_cs_name_cmd);
            flush_list(n);
            return b;
        } else {
            complain_missing_csname();
        }
    }
    /* Look up the characters of list |n| in the hash table, and set |cur_cs| */
    m = first;
    p = token_link(n);
    while (p != null) {
        if (m >= max_buf_stack) {
            max_buf_stack = m + 4;
            if (max_buf_stack >= buf_size)
                check_buffer_overflow(max_buf_stack);
        }
        s = token_chr(token_info(p));
        if (s <= 0x7F) {
            buffer[m++] = (packed_ASCII_code) s;
        } else if (s <= 0x7FF) {
            buffer[m++] = (packed_ASCII_code) (0xC0 + s / 0x40);
            buffer[m++] = (packed_ASCII_code) (0x80 + s % 0x40);
        } else if (s <= 0xFFFF) {
            buffer[m++] = (packed_ASCII_code) (0xE0 + s / 0x1000);
            buffer[m++] = (packed_ASCII_code) (0x80 + (s % 0x1000) / 0x40);
            buffer[m++] = (packed_ASCII_code) (0x80 + (s % 0x1000) % 0x40);
        } else {
            buffer[m++] = (packed_ASCII_code) (0xF0 + s / 0x40000);
            buffer[m++] = (packed_ASCII_code) (0x80 + (s % 0x40000) / 0x1000);
            buffer[m++] =
                (packed_ASCII_code) (0x80 + ((s % 0x40000) % 0x1000) / 0x40);
            buffer[m++] =
                (packed_ASCII_code) (0x80 + ((s % 0x40000) % 0x1000) % 0x40);
        }
        p = token_link(p);
    }
    if (m > first) {
        cur_cs = id_lookup(first, m - first);   /*|no_new_control_sequence| is |true| */
    } else if (m == first) {
        cur_cs = null_cs;       /*the list is empty */
    }
    b = (eq_type(cur_cs) != undefined_cs_cmd);
    flush_list(n);
    return b;
}


@ An active character will be treated as category 13 following
\.{\\if\\noexpand} or following \.{\\ifcat\\noexpand}.

@c
#define get_x_token_or_active_char() do {                             \
        get_x_token();                                                  \
        if (cur_cmd==relax_cmd && cur_chr==no_expand_flag) {            \
            if (is_active_cs(cs_text(cur_cs))) {                        \
                cur_cmd=active_char_cmd;                                \
                cur_chr=active_cs_value(cs_text(cur_tok-cs_token_flag));	\
            }                                                           \
        }                                                               \
    } while (0)


@ A condition is started when the |expand| procedure encounters
an |if_test| command; in that case |expand| reduces to |conditional|,
which is a recursive procedure.
@^recursion@>

@c
void conditional(void)
{
    boolean b;                  /*is the condition true? */
    int r;                      /*relation to be evaluated */
    int m, n;                   /*to be tested against the second operand */
    halfword p, q;              /*for traversing token lists in \.{\\ifx} tests */
    int save_scanner_status;    /*|scanner_status| upon entry */
    halfword save_cond_ptr;     /*|cond_ptr| corresponding to this conditional */
    int this_if;                /*type of this conditional */
    boolean is_unless;          /*was this if preceded by `\.{\\unless}' ? */
    b = false;                  /*default is false, just in case */
    if (int_par(tracing_ifs_code) > 0)
        if (int_par(tracing_commands_code) <= 1)
            show_cur_cmd_chr();
    push_condition_stack();
    save_cond_ptr = cond_ptr;
    is_unless = (cur_chr >= unless_code);
    this_if = cur_chr % unless_code;
    /* Either process \.{\\ifcase} or set |b| to the value of a boolean condition */
    switch (this_if) {
    case if_char_code:
    case if_cat_code:
        /* Test if two characters match */
        get_x_token_or_active_char();
        if ((cur_cmd > active_char_cmd) || (cur_chr > biggest_char)) {  /*not a character */
            m = relax_cmd;
            n = too_big_char;
        } else {
            m = cur_cmd;
            n = cur_chr;
        }
        get_x_token_or_active_char();
        if ((cur_cmd > active_char_cmd) || (cur_chr > biggest_char)) {
            cur_cmd = relax_cmd;
            cur_chr = too_big_char;
        }
        if (this_if == if_char_code)
            b = (n == cur_chr);
        else
            b = (m == cur_cmd);
        break;
    case if_int_code:
    case if_dim_code:
    case if_abs_dim_code:
    case if_abs_num_code:
        /* Test relation between integers or dimensions */
        /* Here we use the fact that |"<"|, |"="|, and |">"| are consecutive ASCII
           codes. */
        if (this_if == if_int_code || this_if == if_abs_num_code)
            scan_int();
        else
            scan_normal_dimen();
        n = cur_val;
        if (n < 0)
            if (this_if == if_abs_dim_code || this_if == if_abs_num_code)
                negate(n);

        /* Get the next non-blank non-call... */
        do {
            get_x_token();
        } while (cur_cmd == spacer_cmd);

        if ((cur_tok >= other_token + '<') && (cur_tok <= other_token + '>')) {
            r = cur_tok - other_token;
        } else {
            print_err("Missing = inserted for ");
            print_cmd_chr(if_test_cmd, this_if);
            help1("I was expecting to see `<', `=', or `>'. Didn't.");
            back_error();
            r = '=';
        }
        if (this_if == if_int_code || this_if == if_abs_num_code)
            scan_int();
        else
            scan_normal_dimen();

        if (cur_val < 0)
            if (this_if == if_abs_dim_code || this_if == if_abs_num_code)
                negate(cur_val);

        switch (r) {
        case '<':
            b = (n < cur_val);
            break;
        case '=':
            b = (n == cur_val);
            break;
        case '>':
            b = (n > cur_val);
            break;
        default:
            b = false;
            break;              /*can't happen */
        }
        break;
    case if_odd_code:
        /* Test if an integer is odd */
        scan_int();
        b = odd(cur_val);
        break;
    case if_vmode_code:
        b = (abs(cur_list.mode_field) == vmode);
        break;
    case if_hmode_code:
        b = (abs(cur_list.mode_field) == hmode);
        break;
    case if_mmode_code:
        b = (abs(cur_list.mode_field) == mmode);
        break;
    case if_inner_code:
        b = (cur_list.mode_field < 0);
        break;
    case if_void_code:
    case if_hbox_code:
    case if_vbox_code:
        /* Test box register status */
        scan_register_num();
        p = box(cur_val);
        if (this_if == if_void_code)
            b = (p == null);
        else if (p == null)
            b = false;
        else if (this_if == if_hbox_code)
            b = (type(p) == hlist_node);
        else
            b = (type(p) == vlist_node);
        break;
    case ifx_code:
        /* Test if two tokens match */
        /* Note that `\.{\\ifx}' will declare two macros different if one is \\{long}
           or \\{outer} and the other isn't, even though the texts of the macros are
           the same.

           We need to reset |scanner_status|, since \.{\\outer} control sequences
           are allowed, but we might be scanning a macro definition or preamble.
         */
        save_scanner_status = scanner_status;
        scanner_status = normal;
        get_token_lua();
        n = cur_cs;
        p = cur_cmd;
        q = cur_chr;
        get_token_lua();
        if (cur_cmd != p) {
            b = false;
        } else if (cur_cmd < call_cmd) {
            b = (cur_chr == q);
        } else {
            /* Test if two macro texts match */
            /* Note also that `\.{\\ifx}' decides that macros \.{\\a} and \.{\\b} are
               different in examples like this:
               $$\vbox{\halign{\.{#}\hfil&\qquad\.{#}\hfil\cr
               {}\\def\\a\{\\c\}&
               {}\\def\\c\{\}\cr
               {}\\def\\b\{\\d\}&
               {}\\def\\d\{\}\cr}}$$ */
            p = token_link(cur_chr);
            q = token_link(equiv(n));   /*omit reference counts */
            if (p == q) {
                b = true;
            } else {
                while ((p != null) && (q != null)) {
                    if (token_info(p) != token_info(q)) {
                        p = null;
                    } else {
                        p = token_link(p);
                        q = token_link(q);
                    }
                }
                b = ((p == null) && (q == null));
            }
        }
        scanner_status = save_scanner_status;
        break;
    case if_eof_code:
        scan_four_bit_int_or_18();
        if (cur_val == 18)
            b = !shellenabledp;
        else
            b = (read_open[cur_val] == closed);
        break;
    case if_true_code:
        b = true;
        break;
    case if_false_code:
        b = false;
        break;
    case if_case_code:
        /* Select the appropriate case
           and |return| or |goto common_ending| */
        scan_int();
        n = cur_val;            /*|n| is the number of cases to pass */
        if (int_par(tracing_commands_code) > 1) {
            begin_diagnostic();
            tprint("{case ");
            print_int(n);
            print_char('}');
            end_diagnostic(false);
        }
        while (n != 0) {
            pass_text();
            if (cond_ptr == save_cond_ptr) {
                if (cur_chr == or_code)
                    decr(n);
                else
                    goto COMMON_ENDING;
            } else if (cur_chr == fi_code) {
                pop_condition_stack();
            }
        }
        change_if_limit(or_code, save_cond_ptr);
        return;                 /*wait for \.{\\or}, \.{\\else}, or \.{\\fi} */
        break;
    case if_primitive_code:
        save_scanner_status = scanner_status;
        scanner_status = normal;
        get_token_lua();
        scanner_status = save_scanner_status;
        m = prim_lookup(cs_text(cur_cs));
        b = ((cur_cmd != undefined_cs_cmd) &&
             (m != undefined_primitive) &&
             (cur_cmd == get_prim_eq_type(m)) &&
             (cur_chr == get_prim_equiv(m)));
        break;
    case if_def_code:
        /* The conditional \.{\\ifdefined} tests if a control sequence is defined. */
        /* We need to reset |scanner_status|, since \.{\\outer} control sequences
           are allowed, but we might be scanning a macro definition or preamble. */
        save_scanner_status = scanner_status;
        scanner_status = normal;
        get_token_lua();
        b = (cur_cmd != undefined_cs_cmd);
        scanner_status = save_scanner_status;
        break;
    case if_cs_code:
        b = test_for_cs();
        break;
    case if_in_csname_code:
        b = is_in_csname;
        break;
    case if_font_char_code:
        /* The conditional \.{\\iffontchar} tests the existence of a character in
           a font. */
        scan_font_ident();
        n = cur_val;
        scan_char_num();
        b = char_exists(n, cur_val);
        break;
    default:                   /* there are no other cases, but for -Wall:  */
        b = false;
    }

    if (is_unless)
        b = !b;
    if (int_par(tracing_commands_code) > 1) {
        /* Display the value of |b| */
        begin_diagnostic();
        if (b)
            tprint("{true}");
        else
            tprint("{false}");
        end_diagnostic(false);
    }
    if (b) {
        change_if_limit(else_code, save_cond_ptr);
        return;                 /*wait for \.{\\else} or \.{\\fi} */
    }
    /* Skip to \.{\\else} or \.{\\fi}, then |goto common_ending| */
    /*
       In a construction like `\.{\\if\\iftrue abc\\else d\\fi}', the first
       \.{\\else} that we come to after learning that the \.{\\if} is false is
       not the \.{\\else} we're looking for. Hence the following curious
       logic is needed.
     */
    while (1) {
        pass_text();
        if (cond_ptr == save_cond_ptr) {
            if (cur_chr != or_code)
                goto COMMON_ENDING;
            print_err("Extra \\or");
            help1("I'm ignoring this; it doesn't match any \\if.");
            error();
        } else if (cur_chr == fi_code) {
            pop_condition_stack();
        }
    }
  COMMON_ENDING:
    if (cur_chr == fi_code)
        pop_condition_stack();
    else
        if_limit = fi_code;     /*wait for \.{\\fi} */
}