retex_engine/

prefixed.rs

//! Assignments (`prefixed_command`, *TeX: The Program* §1211–§1280, with
//! e-TeX and LuaTeX additions).

use std::rc::Rc;

use retex_arith as arith;

use crate::Engine;
use crate::cmd::Cmd;
use crate::eqtb::{CodeKind, Loc, MU_GLUE_OFFSET, Meaning, Val};
use crate::expand::RELAX_CHR;
use crate::glue::Glue;
use crate::hash::{CsId, NO_CS};
use crate::primitives_gen as pg;
use crate::scan::{REG_OFFSET, ValLevel, reg};
use crate::token::{Macro, Token, TokenList};

/// `prefix` modifiers.
pub mod prefix {
    /// `\long`.
    pub const LONG: u32 = 1;
    /// `\outer`.
    pub const OUTER: u32 = 2;
    /// `\global`.
    pub const GLOBAL: u32 = 4;
    /// `\protected`.
    pub const PROTECTED: u32 = 8;
}

/// `shorthand_def` modifiers (LuaTeX numbering).
#[allow(missing_docs)]
pub mod shorthand {
    pub const CHAR_DEF: u32 = 0;
    pub const MATH_CHAR_DEF: u32 = 1;
    pub const UMATH_CHAR_DEF: u32 = 2;
    pub const COUNT_DEF: u32 = 3;
    pub const ATTRIBUTE_DEF: u32 = 4;
    pub const DIMEN_DEF: u32 = 5;
    pub const SKIP_DEF: u32 = 6;
    pub const MU_SKIP_DEF: u32 = 7;
    pub const TOKS_DEF: u32 = 8;
    pub const UMATH_CHAR_NUM_DEF: u32 = 9;
}

impl Engine {
    /// Gets a redefinable control sequence (`get_r_token`).
    pub fn get_r_token(&mut self) {
        loop {
            loop {
                self.get_token();
                if self.cur_tok != Token::SPACE {
                    break;
                }
            }
            let frozen = self.cur_cs != NO_CS
                && matches!(self.hash.kind(self.cur_cs), crate::hash::CsKind::Frozen);
            if self.cur_cs == NO_CS || frozen {
                self.print_err("Missing control sequence inserted");
                self.help(&[
                    "Please don't say `\\def cs{...}', say `\\def\\cs{...}'.",
                    "I've inserted an inaccessible control sequence so that your",
                    "definition will be completed without mixing me up too badly.",
                    "You can recover graciously from this error, if you're",
                    "careful; see exercise 27.2 in The TeXbook.",
                ]);
                if self.cur_cs == NO_CS {
                    self.back_input();
                }
                self.cur_tok = Token::cs(self.cs.frozen_protection);
                self.ins_error();
                continue;
            }
            return;
        }
    }

    /// Defines control sequence `p` with `meaning`.
    fn define_cs(&mut self, global: bool, p: CsId, meaning: Meaning) {
        self.define(global, Loc::Cs(p), Val::Meaning(meaning));
    }

    /// Performs an assignment, possibly prefixed (`prefixed_command`).
    pub fn prefixed_command(&mut self) {
        // Fast path: the most common assignments, without prefixes and
        // with `\globaldefs` zero, skip the general machinery.
        if self.cur_cmd != Cmd::Prefix && self.eqtb.int(pg::assign_int::GLOBALDEFS) == 0 {
            match self.cur_cmd {
                Cmd::Let => self.let_command(false),
                Cmd::DefCharCode => self.def_char_code(false),
                Cmd::Register | Cmd::Advance | Cmd::Multiply | Cmd::Divide => {
                    self.do_register_command(false)
                }
                Cmd::AssignInt => self.assign_int_command(false),
                _ => return self.prefixed_command_general(),
            }
            if self.after_token.0 != 0 {
                self.cur_tok = self.after_token;
                self.back_input();
                self.after_token = Token(0);
            }
            return;
        }
        self.prefixed_command_general();
    }

    /// `\count`-like and integer parameter assignments.
    fn assign_int_command(&mut self, global: bool) {
        let p = self.cur_chr;
        self.scan_optional_equals();
        self.scan_int();
        let loc = if p >= REG_OFFSET {
            Loc::Count(p - REG_OFFSET)
        } else {
            Loc::IntPar(p)
        };
        self.assign_int_param(global, loc, self.cur_val);
    }

    /// [`prefixed_command`](Self::prefixed_command) in general.
    #[inline(never)]
    fn prefixed_command_general(&mut self) {
        let mut a: u32 = 0;
        while self.cur_cmd == Cmd::Prefix {
            if a & self.cur_chr == 0 {
                a += self.cur_chr;
            }
            self.get_nonblank_nonrelax_noncall();
            if self.cur_cmd <= Cmd::MAX_NON_PREFIXED {
                self.print_err("You can't use a prefix with `");
                self.print_cmd_chr(self.cur_cmd, self.cur_chr);
                self.printer.print_char('\'' as u32);
                self.help(&[
                    "I'll pretend you didn't say \\long or \\outer or \\global or",
                    "\\protected.",
                ]);
                self.back_error();
                return;
            }
            if self.eqtb.int(pg::assign_int::TRACINGCOMMANDS) > 2 {
                self.show_cur_cmd_chr();
            }
        }
        // Discard \long, \outer and \protected if irrelevant.
        if self.cur_cmd != Cmd::Def
            && self.cur_cmd != Cmd::DefLuaCall
            && (a & (prefix::LONG | prefix::OUTER | prefix::PROTECTED)) != 0
            && self.eqtb.int(pg::assign_int::SUPPRESSLONGERROR) <= 0
        {
            self.print_err("You can't use `");
            self.print_esc_str("long");
            self.printer.print_str("' or `");
            self.print_esc_str("outer");
            self.help(&["I'll pretend you didn't say \\long or \\outer or \\protected here."]);
            self.printer.print_str("' or `");
            self.print_esc_str("protected");
            self.printer.print_str("' with `");
            self.print_cmd_chr(self.cur_cmd, self.cur_chr);
            self.printer.print_char('\'' as u32);
            self.error();
        }
        // Adjust for \globaldefs.
        let global_defs = self.eqtb.int(pg::assign_int::GLOBALDEFS);
        if global_defs != 0 {
            if global_defs < 0 {
                a &= !prefix::GLOBAL;
            } else {
                a |= prefix::GLOBAL;
            }
        }
        let global = a & prefix::GLOBAL != 0;
        match self.cur_cmd {
            Cmd::SetFont => {
                let f = self.cur_chr;
                self.define(global, Loc::CurFont, Val::Int(i64::from(f)));
            }
            Cmd::Def => {
                let mut a = a;
                if self.cur_chr & 1 != 0 && !global && global_defs >= 0 {
                    a |= prefix::GLOBAL;
                }
                let e = self.cur_chr >= 2;
                self.get_r_token();
                let p = self.cur_cs;
                self.def_ref_cs = p;
                let toks = self.scan_toks(true, e);
                self.def_ref_cs = NO_CS;
                let cmd = Cmd::from_u8(Cmd::Call as u8 + (a & 3) as u8);
                let mac = Macro {
                    protected: a & prefix::PROTECTED != 0,
                    tokens: Rc::from(toks),
                };
                self.define_cs(
                    a & prefix::GLOBAL != 0,
                    p,
                    Meaning {
                        cmd,
                        chr: 0,
                        mac: Some(Rc::new(mac)),
                    },
                );
            }
            Cmd::Let => self.let_command(global),
            Cmd::ShorthandDef => self.shorthand_def(global),
            Cmd::ReadToCs => {
                let j = self.cur_chr;
                self.scan_int();
                let n = self.cur_val;
                if !self.scan_keyword("to") {
                    self.print_err("Missing `to' inserted");
                    self.help(&[
                        "You should have said `\\read<number> to \\cs'.",
                        "I'm going to look for the \\cs now.",
                    ]);
                    self.error();
                }
                self.get_r_token();
                let p = self.cur_cs;
                let toks = self.read_toks(n, p, j);
                self.define_cs(
                    global,
                    p,
                    Meaning {
                        cmd: Cmd::Call,
                        chr: 0,
                        mac: Some(Rc::new(Macro {
                            protected: false,
                            tokens: Rc::from(toks),
                        })),
                    },
                );
            }
            Cmd::ToksRegister | Cmd::AssignToks => self.assign_toks(global),
            Cmd::Combinetoks => self.combine_toks(),
            Cmd::AssignInt => self.assign_int_command(global),
            Cmd::AssignAttr => {
                let p = self.cur_chr - REG_OFFSET.min(self.cur_chr);
                self.scan_optional_equals();
                self.scan_int();
                self.define(global, Loc::Attr(p), Val::Int(i64::from(self.cur_val)));
            }
            Cmd::AssignDir | Cmd::AssignDirection => {
                let p = self.cur_chr;
                let by_name = self.cur_cmd == Cmd::AssignDir;
                self.scan_optional_equals();
                let d = if by_name {
                    self.scan_direction_spec()
                } else {
                    self.scan_int();
                    self.cur_val
                };
                self.assign_dir_param(global, p, d);
                if p == crate::primitives_gen::assign_dir::TEXTDIR {
                    self.text_dir_assigned(d);
                }
            }
            Cmd::AssignDimen => {
                let p = self.cur_chr;
                self.scan_optional_equals();
                self.scan_normal_dimen();
                let loc = if p >= REG_OFFSET {
                    Loc::Dimen(p - REG_OFFSET)
                } else {
                    Loc::DimenPar(p)
                };
                self.define(global, loc, Val::Int(i64::from(self.cur_val)));
            }
            Cmd::AssignGlue | Cmd::AssignMuGlue => {
                let p = self.cur_chr;
                let mu = self.cur_cmd == Cmd::AssignMuGlue;
                self.scan_optional_equals();
                self.scan_glue(if mu { ValLevel::Mu } else { ValLevel::Glue });
                let g = self.cur_glue;
                let loc = match (mu, p >= REG_OFFSET) {
                    (false, true) => Loc::Skip(p - REG_OFFSET),
                    (true, true) => Loc::MuSkip(p - REG_OFFSET),
                    (false, false) => Loc::GluePar(p),
                    (true, false) => Loc::GluePar(p + MU_GLUE_OFFSET),
                };
                self.define(global, loc, Val::Glue(g));
            }
            Cmd::DefCharCode => self.def_char_code(global),
            Cmd::DefDelCode => {
                self.scan_char_num();
                let c = self.cur_val as u32;
                self.scan_optional_equals();
                self.scan_int();
                let v = self.cur_val;
                if v > 0o77777777 {
                    self.invalid_code(v, 0o77777777, false);
                }
                let code = crate::codes::delcode_from_classic(self.cur_val);
                self.define(global, Loc::Code(CodeKind::Del, c), Val::Int(code));
            }
            Cmd::ExtdefMathCode => {
                let num = self.cur_chr != pg::extdef_math_code::UMATHCODE;
                self.scan_char_num();
                let c = self.cur_val as u32;
                self.scan_optional_equals();
                let code = if num {
                    self.scan_int();
                    i64::from(self.cur_val)
                } else {
                    self.scan_umath_triple()
                };
                self.define(global, Loc::Code(CodeKind::Math, c), Val::Int(code));
            }
            Cmd::ExtdefDelCode => {
                let num = self.cur_chr != pg::extdef_del_code::UDELCODE;
                self.scan_char_num();
                let c = self.cur_val as u32;
                self.scan_optional_equals();
                let code = if num {
                    self.scan_int();
                    i64::from(self.cur_val)
                } else {
                    self.scan_math_family();
                    let fam = self.cur_val as i64;
                    self.scan_char_num();
                    (fam << 21) + i64::from(self.cur_val)
                };
                self.define(global, Loc::Code(CodeKind::Del, c), Val::Int(code));
            }
            Cmd::DefFamily => {
                let size = self.cur_chr;
                self.scan_math_family();
                let fam = self.cur_val as u32;
                self.scan_optional_equals();
                self.scan_font_ident();
                let f = self.cur_val;
                self.define(
                    global,
                    Loc::MathFont(size * crate::eqtb::NUM_FAMILIES as u32 + fam),
                    Val::Int(i64::from(f)),
                );
                self.set_font_math_params(global, size, fam, f as u32);
            }
            Cmd::SetMathParam => {
                let p = self.cur_chr;
                let _ = self.scan_math_style();
                let style = self.cur_val as u32;
                self.scan_optional_equals();
                let v = if crate::codes::math_param_is_glue(p) {
                    self.scan_glue(ValLevel::Mu);
                    self.store_math_param_glue(self.cur_glue)
                } else if p == crate::mathparams::mp::RADICAL_DEGREE_RAISE {
                    self.scan_int();
                    self.cur_val
                } else {
                    self.scan_normal_dimen();
                    self.cur_val
                };
                self.define(
                    global,
                    Loc::MathParam(p * 8 + style),
                    Val::Int(i64::from(v)),
                );
            }
            Cmd::Register | Cmd::Advance | Cmd::Multiply | Cmd::Divide => {
                self.do_register_command(global)
            }
            Cmd::SetBox => {
                self.scan_register_num();
                let n = self.cur_val as u32;
                let ctx = if global {
                    crate::maincontrol::BoxContext::GlobalSetBox(n)
                } else {
                    crate::maincontrol::BoxContext::SetBox(n)
                };
                self.scan_optional_equals();
                if self.err.set_box_allowed {
                    self.scan_box(ctx);
                } else {
                    self.print_err("Improper ");
                    self.print_esc_str("setbox");
                    self.help(&[
                        "Sorry, \\setbox is not allowed after \\halign in a display,",
                        "or between \\accent and an accented character.",
                    ]);
                    self.error();
                }
            }
            Cmd::SetAux => self.alter_aux(),
            Cmd::SetPrevGraf => self.alter_prev_graf(),
            Cmd::SetPageDimen => self.alter_page_so_far(),
            Cmd::SetPageInt => self.alter_integer(),
            Cmd::SetBoxDimen => self.alter_box_dimen(),
            Cmd::SetTexShape => {
                self.scan_optional_equals();
                self.scan_int();
                let n = self.cur_val;
                let shape = if n <= 0 {
                    None
                } else {
                    let mut v = Vec::with_capacity(2 * n as usize);
                    for _ in 0..n {
                        self.scan_normal_dimen();
                        v.push(self.cur_val);
                        self.scan_normal_dimen();
                        v.push(self.cur_val);
                    }
                    Some(Rc::from(v))
                };
                self.define(global, Loc::ParShape, Val::Shape(shape));
            }
            Cmd::SetEtexShape => {
                let q = self.cur_chr;
                self.scan_optional_equals();
                self.scan_int();
                let n = self.cur_val;
                let shape = if n <= 0 {
                    None
                } else {
                    let mut v = Vec::with_capacity(n as usize);
                    for _ in 0..n {
                        self.scan_int();
                        v.push(self.cur_val);
                    }
                    Some(Rc::from(v))
                };
                self.define(global, Loc::EtexShape(q), Val::Shape(shape));
            }
            Cmd::HyphData => self.hyph_data(global),
            Cmd::AssignFontDimen => {
                self.find_font_dimen(true);
                let loc = self.font_dimen_loc;
                self.scan_optional_equals();
                self.scan_normal_dimen();
                self.set_font_dimen(loc, self.cur_val);
            }
            Cmd::AssignFontInt => {
                let n = self.cur_chr;
                self.scan_font_ident();
                let f = self.cur_val as u32;
                if (2..=5).contains(&n) {
                    // \lpcode, \rpcode, \efcode, \tagcode take a character.
                    self.scan_char_num();
                    let c = self.cur_val as u32;
                    self.scan_optional_equals();
                    self.scan_int();
                    self.set_font_char_code(f, n, c, self.cur_val);
                } else {
                    self.scan_optional_equals();
                    self.scan_int();
                    self.set_font_int_param(f, n, self.cur_val);
                }
            }
            Cmd::DefFont => self.new_font(global),
            Cmd::LetterspaceFont => self.letterspace_font(global),
            Cmd::CopyFont => self.copy_font(global),
            Cmd::SetFontId => {
                self.scan_int();
                let f = self.cur_val;
                if self.font_exists(f) {
                    self.define(global, Loc::CurFont, Val::Int(i64::from(f)));
                }
            }
            Cmd::SetInteraction => self.new_interaction(),
            Cmd::DefLuaCall => self.def_lua_call(global, a & prefix::PROTECTED != 0),
            Cmd::AssignBoxDir | Cmd::AssignBoxDirection => {
                self.scan_register_num();
                let n = self.cur_val as u32;
                self.scan_optional_equals();
                let d = if self.cur_cmd == Cmd::AssignBoxDir {
                    self.scan_direction_spec()
                } else {
                    self.scan_int();
                    self.cur_val
                };
                self.set_box_dir(n, d);
            }
            _ => self.confusion("prefix"),
        }
        // Insert a token saved by \afterassignment, if any.
        if self.after_token.0 != 0 {
            self.cur_tok = self.after_token;
            self.back_input();
            self.after_token = Token(0);
        }
    }

    fn assign_int_param(&mut self, global: bool, loc: Loc, v: i32) {
        self.define(global, loc, Val::Int(i64::from(v)));
        if let Loc::IntPar(i) = loc {
            self.int_param_changed(i);
        }
    }

    /// Hooks for integer parameters with side effects (`\newlinechar`, …).
    pub fn int_param_changed(&mut self, i: u32) {
        if i == pg::assign_int::NEWLINECHAR {
            self.printer.new_line_char = self.eqtb.int(i);
        } else if i == pg::assign_int::SYNCTEX {
            self.synctex_changed();
        }
    }

    /// `\let`, `\glet`, `\futurelet`, `\letcharcode`.
    fn let_command(&mut self, global: bool) {
        let n = self.cur_chr;
        let mut global = global;
        if n == 3 {
            // \letcharcode <char> = <cs>: defines the active character.
            self.scan_int();
            let c = self.cur_val;
            if !(1..=0x10_FFFF).contains(&c) {
                self.print_err("invalid number for \\letcharcode");
                self.help(&[]);
                self.error();
                return;
            }
            let p = self.hash.active(c as u32);
            self.scan_optional_equals();
            self.get_token();
            let m = self.token_meaning();
            self.define_cs(global, p, m);
            return;
        }
        if n == 0 {
            global = true; // \glet
        }
        self.get_r_token();
        let p = self.cur_cs;
        if n <= 1 {
            loop {
                self.get_token();
                if self.cur_cmd != Cmd::Spacer {
                    break;
                }
            }
            if self.cur_tok == Token::other('=' as u32) {
                self.get_token();
                if self.cur_cmd == Cmd::Spacer {
                    self.get_token();
                }
            }
        } else {
            self.get_token();
            let q = self.cur_tok;
            self.get_token();
            self.back_input();
            self.cur_tok = q;
            self.back_input(); // back_input does not change cur_cmd/cur_chr
        }
        let m = self.token_meaning();
        self.define_cs(global, p, m);
    }

    /// The meaning of the current token, for `\let`.
    fn token_meaning(&self) -> Meaning {
        if self.cur_cs != NO_CS {
            let mut m = self.eqtb.meaning(self.cur_cs).clone();
            // `cur_cmd`/`cur_chr` may differ from the eqtb entry for
            // \noexpand'ed tokens; follow TeX and use them.
            if m.cmd != self.cur_cmd {
                m = Meaning::prim(self.cur_cmd, self.cur_chr);
            }
            m
        } else {
            Meaning::prim(self.cur_cmd, self.cur_chr)
        }
    }

    /// `\chardef` and friends.
    fn shorthand_def(&mut self, global: bool) {
        let n = self.cur_chr;
        self.get_r_token();
        let p = self.cur_cs;
        self.define_cs(global, p, Meaning::prim(Cmd::Relax, RELAX_CHR));
        self.scan_optional_equals();
        let m = match n {
            shorthand::CHAR_DEF => {
                self.scan_char_num();
                Meaning::prim(Cmd::CharGiven, self.cur_val as u32)
            }
            shorthand::MATH_CHAR_DEF => {
                // Kept in TeX's 15-bit form, as LuaTeX shows and reads it.
                let g = self.scan_math_given();
                Meaning::prim(Cmd::MathGiven, g)
            }
            shorthand::UMATH_CHAR_DEF => {
                let code = self.scan_umath_triple();
                Meaning::prim(Cmd::XmathGiven, code as u32)
            }
            shorthand::UMATH_CHAR_NUM_DEF => {
                self.scan_int();
                Meaning::prim(Cmd::XmathGiven, self.cur_val as u32)
            }
            _ => {
                self.scan_register_num();
                let r = self.cur_val as u32 + REG_OFFSET;
                match n {
                    shorthand::COUNT_DEF => Meaning::prim(Cmd::AssignInt, r),
                    shorthand::ATTRIBUTE_DEF => Meaning::prim(Cmd::AssignAttr, r),
                    shorthand::DIMEN_DEF => Meaning::prim(Cmd::AssignDimen, r),
                    shorthand::SKIP_DEF => Meaning::prim(Cmd::AssignGlue, r),
                    shorthand::MU_SKIP_DEF => Meaning::prim(Cmd::AssignMuGlue, r),
                    _ => Meaning::prim(Cmd::AssignToks, r),
                }
            }
        };
        self.define_cs(global, p, m);
    }

    /// Scans `class family char` for `\Umathcode` and `\Umathchardef`.
    pub(crate) fn scan_umath_triple(&mut self) -> i64 {
        self.scan_int();
        let class = self.cur_val;
        self.scan_math_family();
        let fam = self.cur_val;
        self.scan_char_num();
        let chr = self.cur_val;
        if !(0..=7).contains(&class) {
            self.print_err("Invalid math code");
            self.help(&["I'm going to use 0 instead of that illegal code value."]);
            self.error();
            return 0;
        }
        crate::codes::math_code(class as u32, fam as u32, chr as u32)
    }

    /// `\toks`, `\everypar` and other token-list assignments.
    fn assign_toks(&mut self, global: bool) {
        let q = self.cur_cs;
        let loc = if self.cur_cmd == Cmd::ToksRegister {
            self.scan_register_num();
            Loc::Toks(self.cur_val as u32)
        } else if self.cur_chr >= REG_OFFSET {
            Loc::Toks(self.cur_chr - REG_OFFSET)
        } else {
            Loc::ToksPar(self.cur_chr)
        };
        self.scan_optional_equals();
        self.get_nonblank_nonrelax_noncall();
        if self.cur_cmd != Cmd::LeftBrace {
            // The right-hand side may be a token parameter or register.
            let src = if self.cur_cmd == Cmd::ToksRegister {
                self.scan_register_num();
                Some(self.eqtb.toks[self.cur_val as usize].val.clone())
            } else if self.cur_cmd == Cmd::AssignToks {
                Some(if self.cur_chr >= REG_OFFSET {
                    self.eqtb.toks[(self.cur_chr - REG_OFFSET) as usize]
                        .val
                        .clone()
                } else {
                    self.eqtb.toks_param(self.cur_chr).clone()
                })
            } else {
                None
            };
            if let Some(list) = src {
                self.define(global, loc, Val::Toks(list));
                return;
            }
        }
        self.back_input();
        self.cur_cs = q;
        self.def_ref_cs = q;
        let mut toks = self.scan_toks(false, false);
        self.def_ref_cs = NO_CS;
        if !toks.is_empty() && loc == Loc::ToksPar(pg::assign_toks::OUTPUT) {
            toks.insert(0, Token::LEFT_BRACE);
            toks.push(Token::RIGHT_BRACE);
        }
        let list: TokenList = if toks.is_empty() {
            crate::token::empty_list()
        } else {
            Rc::from(toks)
        };
        self.define(global, loc, Val::Toks(list));
    }

    /// LuaTeX's `\toksapp`, `\etoksapp`, `\tokspre`, … (`combinetoks`).
    fn combine_toks(&mut self) {
        let code = self.cur_chr;
        let global = code >= 4;
        let expand = code % 2 == 1;
        let append = code % 4 < 2;
        // The target: a register number or a token register control
        // sequence.
        self.get_nonblank_nonrelax_noncall();
        let loc = if self.cur_cmd == Cmd::AssignToks {
            if self.cur_chr >= REG_OFFSET {
                Loc::Toks(self.cur_chr - REG_OFFSET)
            } else {
                Loc::ToksPar(self.cur_chr)
            }
        } else if self.cur_cmd == Cmd::ToksRegister {
            self.scan_register_num();
            Loc::Toks(self.cur_val as u32)
        } else {
            self.back_input();
            self.scan_register_num();
            Loc::Toks(self.cur_val as u32)
        };
        let new = if expand {
            self.scan_toks_expanded()
        } else {
            self.scan_general_text().to_vec()
        };
        let old = match self.eqtb.get(loc) {
            Val::Toks(t) => t,
            _ => crate::token::empty_list(),
        };
        let mut v: Vec<Token> = Vec::with_capacity(old.len() + new.len());
        if append {
            v.extend_from_slice(&old);
            v.extend_from_slice(&new);
        } else {
            v.extend_from_slice(&new);
            v.extend_from_slice(&old);
        }
        self.define(global, loc, Val::Toks(Rc::from(v)));
    }

    fn invalid_code(&mut self, v: i32, n: i32, range: bool) {
        self.print_err("Invalid code (");
        self.printer.print_int(v.into());
        if range {
            self.printer.print_str("), should be in the range 0..");
        } else {
            self.printer.print_str("), should be at most ");
        }
        self.printer.print_int(n.into());
        self.help(&["I'm going to use 0 instead of that illegal code value."]);
        self.error();
        self.cur_val = 0;
    }

    /// `\catcode`, `\lccode`, `\uccode`, `\sfcode`, `\mathcode`.
    fn def_char_code(&mut self, global: bool) {
        use pg::def_char_code as dc;
        let which = self.cur_chr;
        let n: i32 = match which {
            dc::CATCODE => 15,
            dc::MATHCODE => 0x8000,
            dc::SFCODE => 0o77777,
            _ => 0x10_FFFF,
        };
        self.scan_char_num();
        let c = self.cur_val as u32;
        self.scan_optional_equals();
        self.scan_int();
        if self.cur_val < 0 || self.cur_val > n {
            self.invalid_code(self.cur_val, n, true);
        }
        let v = self.cur_val;
        match which {
            dc::CATCODE => {
                let table = self.eqtb.cur_cat_table();
                self.define(global, Loc::Cat { table, ch: c }, Val::Int(i64::from(v)));
            }
            dc::LCCODE => self.define(global, Loc::Code(CodeKind::Lc, c), Val::Int(v.into())),
            dc::UCCODE => self.define(global, Loc::Code(CodeKind::Uc, c), Val::Int(v.into())),
            dc::SFCODE => self.define(global, Loc::Code(CodeKind::Sf, c), Val::Int(v.into())),
            _ => {
                let code = if v == 0x8000 {
                    crate::codes::MATH_ACTIVE
                } else {
                    let v = v as u32;
                    crate::codes::math_code(v >> 12, (v >> 8) & 0xF, v & 0xFF)
                };
                self.define(global, Loc::Code(CodeKind::Math, c), Val::Int(code));
            }
        }
    }

    /// `\count`, `\advance`, `\multiply`, `\divide` (`do_register_command`).
    fn do_register_command(&mut self, global: bool) {
        let q = self.cur_cmd;
        // Compute the register location and its type.
        let (loc, p): (Loc, ValLevel) = 'found: {
            if q != Cmd::Register {
                self.get_x_token();
                let r = self.cur_chr;
                let l = match self.cur_cmd {
                    Cmd::AssignInt => Some((
                        if r >= REG_OFFSET {
                            Loc::Count(r - REG_OFFSET)
                        } else {
                            Loc::IntPar(r)
                        },
                        ValLevel::Int,
                    )),
                    Cmd::AssignAttr => Some((Loc::Attr(r - REG_OFFSET.min(r)), ValLevel::Int)),
                    Cmd::AssignDimen => Some((
                        if r >= REG_OFFSET {
                            Loc::Dimen(r - REG_OFFSET)
                        } else {
                            Loc::DimenPar(r)
                        },
                        ValLevel::Dimen,
                    )),
                    Cmd::AssignGlue => Some((
                        if r >= REG_OFFSET {
                            Loc::Skip(r - REG_OFFSET)
                        } else {
                            Loc::GluePar(r)
                        },
                        ValLevel::Glue,
                    )),
                    Cmd::AssignMuGlue => Some((
                        if r >= REG_OFFSET {
                            Loc::MuSkip(r - REG_OFFSET)
                        } else {
                            Loc::GluePar(r + MU_GLUE_OFFSET)
                        },
                        ValLevel::Mu,
                    )),
                    _ => None,
                };
                if let Some(x) = l {
                    break 'found x;
                }
                if self.cur_cmd != Cmd::Register {
                    self.print_err("You can't use `");
                    self.print_cmd_chr(self.cur_cmd, self.cur_chr);
                    self.printer.print_str("' after ");
                    self.print_cmd_chr(q, 0);
                    self.help(&["I'm forgetting what you said and not changing anything."]);
                    self.error();
                    return;
                }
            }
            let kind = self.cur_chr;
            self.scan_register_num();
            let n = self.cur_val as u32;
            match kind {
                reg::COUNT => (Loc::Count(n), ValLevel::Int),
                reg::ATTRIBUTE => (Loc::Attr(n), ValLevel::Int),
                reg::DIMEN => (Loc::Dimen(n), ValLevel::Dimen),
                reg::SKIP => (Loc::Skip(n), ValLevel::Glue),
                _ => (Loc::MuSkip(n), ValLevel::Mu),
            }
        };
        if q == Cmd::Register {
            self.scan_optional_equals();
        } else {
            let _ = self.scan_keyword("by");
        }
        let mut arith_error = false;
        let old = self.eqtb.get(loc);
        let result: Val = if q < Cmd::Multiply {
            if p < ValLevel::Glue {
                if p == ValLevel::Int {
                    self.scan_int();
                } else {
                    self.scan_normal_dimen();
                }
                let mut v = self.cur_val;
                if q == Cmd::Advance
                    && let Val::Int(o) = old
                {
                    v = v.wrapping_add(o as i32);
                }
                Val::Int(i64::from(v))
            } else {
                self.scan_glue(p);
                let mut g = self.cur_glue;
                if q == Cmd::Advance
                    && let Val::Glue(r) = old
                {
                    g = add_glue(g, r);
                }
                Val::Glue(g)
            }
        } else {
            self.scan_int();
            let f = self.cur_val;
            let op = |x: i32, err: &mut bool| -> i32 {
                let r = if q == Cmd::Multiply {
                    if p == ValLevel::Int {
                        arith::mult_integers(x, f)
                    } else {
                        arith::nx_plus_y(x, f, 0)
                    }
                } else {
                    arith::x_over_n(x, f).map(|d| d.quotient)
                };
                r.unwrap_or_else(|_| {
                    *err = true;
                    0
                })
            };
            match old {
                Val::Int(x) => Val::Int(i64::from(op(x as i32, &mut arith_error))),
                Val::Glue(g) => {
                    let mut n = g;
                    n.width = op(g.width, &mut arith_error);
                    n.stretch = op(g.stretch, &mut arith_error);
                    n.shrink = op(g.shrink, &mut arith_error);
                    Val::Glue(n)
                }
                other => other,
            }
        };
        if arith_error {
            self.print_err("Arithmetic overflow");
            self.help(&[
                "I can't carry out that multiplication or division,",
                "since the result is out of range.",
            ]);
            self.error();
            return;
        }
        self.define(global, loc, result);
    }

    /// `\batchmode` etc. (`new_interaction`).
    pub fn new_interaction(&mut self) {
        self.printer.print_ln();
        self.err.interaction = crate::error::Interaction::from_i32(self.cur_chr as i32);
        self.printer.selector = match (self.err.interaction, self.printer.log_opened()) {
            (crate::error::Interaction::Batch, true) => crate::print::Selector::LogOnly,
            (crate::error::Interaction::Batch, false) => crate::print::Selector::NoPrint,
            (_, true) => crate::print::Selector::TermAndLog,
            (_, false) => crate::print::Selector::TermOnly,
        };
    }

    /// `\deadcycles`, `\insertpenalties`, `\interactionmode`
    /// (`alter_integer`).
    fn alter_integer(&mut self) {
        let c = self.cur_chr;
        self.scan_optional_equals();
        self.scan_int();
        match c {
            0 => self.dead_cycles = self.cur_val,
            1 => self.insert_penalties = self.cur_val,
            _ => {
                if (0..=3).contains(&self.cur_val) {
                    self.cur_chr = self.cur_val as u32;
                    self.new_interaction();
                } else {
                    self.print_err("Bad interaction mode (");
                    self.printer.print_int(self.cur_val.into());
                    self.printer.print_char(')' as u32);
                    self.help(&[
                        "Modes are 0=batch, 1=nonstop, 2=scroll, and",
                        "3=errorstop. Proceed, and I'll ignore this case.",
                    ]);
                    self.int_error(self.cur_val);
                }
            }
        }
    }
}

/// Adds glue `r` to `q` (TeX's "Compute the sum of two glue specs").
pub fn add_glue(mut q: Glue, r: Glue) -> Glue {
    q.width = q.width.wrapping_add(r.width);
    if q.stretch == 0 {
        q.stretch_order = crate::glue::NORMAL;
    }
    if q.stretch_order == r.stretch_order {
        q.stretch = q.stretch.wrapping_add(r.stretch);
    } else if q.stretch_order < r.stretch_order && r.stretch != 0 {
        q.stretch = r.stretch;
        q.stretch_order = r.stretch_order;
    }
    if q.shrink == 0 {
        q.shrink_order = crate::glue::NORMAL;
    }
    if q.shrink_order == r.shrink_order {
        q.shrink = q.shrink.wrapping_add(r.shrink);
    } else if q.shrink_order < r.shrink_order && r.shrink != 0 {
        q.shrink = r.shrink;
        q.shrink_order = r.shrink_order;
    }
    q
}