LaTeX: To make all (generalized) fractions be prefixed with \Ustack, to enable \mathstyle to work right

bxluaustack.sty

% bxluaustack.sty

%% package declaration
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxluaustack}[2015/01/31 v0.2]

%% preparation
\def\bxluy@pkgname{bxluaustack}
\providecommand\bxDebug[1]{}

%--------------------------------------- environment check

%% engine check
\RequirePackage{ifluatex}
\ifluatex\else
  \PackageError\bxluy@pkgname{%
    This package requires LuaTeX}%
    {Package loading is aborted.\MessageBreak\@ehc}
\expandafter\endinput\fi\relax

%--------------------------------------- settings

%%<+> \UstackifyDone
\let\UstackifyDone\@undefined

%% \bxluy@gfp@list
\def\bxluy@gfp@list{%
  \do\over\@@over
  \do\atop\@@atop
  \do\above\@@above
  \do\overwithdelims\@@overwithdelims
  \do\atopwithdelims\@@atopwithdelims
  \do\abovewithdelims\@@abovewithdelims
}

%% \bxluy@unknown@pkg@list
\def\bxluy@unknown@pkg@list{%
  \do{cmathml}%
  \do{tex4ht}%
  \do{typehtml}%
}

%% \bxluy@incompat@pkg@list
\def\bxluy@incompat@pkg@list{%
  \do{amstex}% obsolete
  \do{codepage}% useless in LuaLaTeX
  \do{easyeqn}%
  \do{nath}% FIXME
}

%--------------------------------------- helpers

%% packages
\RequirePackage{etoolbox}[2011/01/03]
\RequirePackage{amsmath}

%% variables
\newbool{bxluy@ok}

%% unique tokens
\def\bxluy@end{\bxluy@end@}

%% \bxluy@initialize
% The begin-document hook.
\@onlypreamble\bxluy@initialize
\let\bxluy@initialize\@empty
\AtBeginDocument{\bxluy@initialize}

%% LuaTeX primitives
\directlua{
  tex.enableprimitives('', {
    'mathstyle', 'Ustack',
    'crampeddisplaystyle', 'crampedtextstyle',
    'crampedscriptstyle', 'crampedscriptscriptstyle'
  })
}

%% \bxluy@Ustack
\let\bxluy@Ustack\Ustack

%--------------------------------------- compatibility stuffs

%% \bxluy@prohibit@gfp
\@onlypreamble\bxluy@prohibit@gfp
\begingroup\catcode`\#=12
\gdef\bxluy@prohibit@gfp{%
\bxDebug{\string\bxluy@prohibit@gfp}%
  \expandafter\patchcmd\csname  primfrac \endcsname
    {\PackageWarning{amsmath}}%
    {\bxluy@err@ivgfp{#1}\@gobble}%
    {\bxluy@oktrue}{\bxluy@okfalse}%
  \unless\ifbxluy@ok
    \PackageError\bxluy@pkgname{%
      Patch to 'amsmath' failed}\@ehc
  \fi}
\endgroup
\def\bxluy@err@ivgfp#1{%
  \PackageError\bxluy@pkgname{%
    Foreign command '\@backslashchar#1' is prohibited}%
   {You should use \noexpand\frac or \noexpand\genfrac
    instead.\MessageBreak\@ehc}}

%% \bxluy@ustackify
\@onlypreamble\bxluy@ustackify
\def\bxluy@ustackify{%
\bxDebug{\string\bxluy@ustackify}%
  \bxluy@ustackify@a
  \ifbxluy@ok
    \DeclareRobustCommand{\frac}[2]{%
      \bxluy@Ustack{\begingroup##1\endgroup\@@over##2}}
  \else
    \PackageError\bxluy@pkgname{%
      Patch to 'amsmath' failed}\@ehc
  \fi}
\@onlypreamble\bxluy@ustackify@a
\begingroup\catcode`\#=12
\gdef\bxluy@ustackify@a{%
  \patchcmd\@genfrac
    {#1}%
    {#1\bxluy@Ustack}%
    {\bxluy@oktrue}{\bxluy@okfalse}}%
\endgroup

%%
\gappto\bxluy@initialize{%
  \bxluy@oktrue
  % check for incompatible packages
  \def\do#1{%
\bxDebug{check for '#1'}%
    \@ifpackageloaded{#1}{%
      \PackageError\bxluy@pkgname{%
        Incompatible package '#1' is loaded}\@ehc
      \bxluy@okfalse
    }{}}%
  \bxluy@incompat@pkg@list
  % check for 'unknown' packages
  \ifbxluy@ok
    \def\do#1{%
\bxDebug{check for '#1'}%
      \@ifpackageloaded{#1}{%
        \PackageWarning\bxluy@pkgname{%
          Prohibition of Fraction primitives is suppressed\MessageBrfeak
          for compatibility with package '#1';\MessageBrfeak
          \noexpand\mathstyle might not work correctly\@gobble}%
        \bxluy@okfalse
      }{}}%
    \ifbxluy@ok
      \bxluy@prohibit@gfp
    \else \bxluy@oktrue
    \fi
  \fi
  \ifbxluy@ok
    \bxluy@ustackify
  \fi
  \ifbxluy@ok
    \let\UstackifyDone=t\relax
  \fi}

%--------------------------------------- compatibility stuffs

%% variables
\newbool{bxluy@patchok}

%% \bxluy@restore@gfp
\def\bxluy@restore@gfp{%
  \let\do\let \bxluy@gfprimes}

%% \bxluy@patched@pkg@list
\let\bxluy@patched@pkg@list\@empty

%% \bxluy@declare@patch
\@onlypreamble\bxluy@declare@patch
\def\bxluy@declare@patch#1{%
  \gappto\bxluy@patched@pkg@list{\do{#1}}%
  \expandafter\bxluy@declare@patch@a\csname bxluy@patch/#1\endcsname}
\@onlypreamble\bxluy@declare@patch@a
\def\bxluy@declare@patch@a#1{%
  \@onlypreamble#1%
  \begingroup \catcode`\#=12
    \def\next{\xdef#1{\the\toks@}\endgroup}%
    \afterassignment\next \toks@=}

%% 'schemata'
\bxluy@declare@patch{schemata}{%
  \patchcmd\complexlbrace
    {$\left}%
    {\bxluy@restore@gfp$\left}%
    {}{\bxluy@okfalse}%
  \patchcmd\complexlbrace
    {$\vbox}%
    {\bxluy@restore@gfp$\vbox}%
    {}{\bxluy@okfalse}}
%% 'oz'
\bxluy@declare@patch{oz}{%
  \patchcmd\z@rename
    {#1 \over #2}%
    {\bxluy@Ustack{#1 \@@over #2}}%
    {}{\bxluy@okfalse}}
%% 'permute'
\bxluy@declare@patch{permute}{%
  \patchcmd\pmt@PrintVPmt@
    {{\pmt@preimage\atop\pmt@image}}%
    {\bxluy@Ustack{\pmt@preimage\@@atop\pmt@image}}%
    {}{\bxluy@okfalse}}
%% 'mafr'
\bxluy@declare@patch{mafr}{%
  \patchcmd\frc
    {{#1\over#2}}%
    {\bxluy@Ustack{#1\@@over#2}}%
    {}{\bxluy@okfalse}}
%% 'slides-class'
\gappto\bxluy@initialize{%
  \csletcs{ver@slides-class.sty}{ver@slides.cls}}
\bxluy@declare@patch{slides-class}{%
  \patchcmd\frc
    {{\begingroup#3\endgroup\over#4}}%
    {\bxluy@Ustack{\begingroup#3\endgroup\@@over#4}}%
    {}{\bxluy@okfalse}}

%%
\gappto\bxluy@initialize{%
  \ifbxluy@ok
    \bxluy@patchoktrue
    \def\do#1{%
\bxDebug{check for '#1'}%
      \@ifpackageloaded{#1}{%
        \bxluy@oktrue
        \csuse{bxluy@patch/#1}%
        \ifbxluy@ok
\bxDebug{ok}%
          \PackageInfo\bxluy@pkgname{%
            Patch applied to package '#1'\@gobble}%
        \else
          \PackageWarning\bxluy@pkgname{%
            Patch to package '#1' failed\@gobble}%
          \bxluy@patchokfalse
        \fi
      }{}}%
    \bxluy@patched@pkg@list
    \unless\ifbxluy@patchok
      \PackageError\bxluy@pkgname{%
        Some necessary patches failed;\MessageBreak
        \noexpand\mathstyle might not work correctly}\@ehc
      \bxluy@okfalse
    \fi
  \fi
  \ifbxluy@ok
    \PackageInfo\bxluy@pkgname{%
      Ustackifying process successfully finished\@gobble}%
  \else\ifdefined\UstackifyDone
    \PackageWarning\bxluy@pkgname{%
      Ustackifying process finished but was incomplete;\MessageBreak
      \noexpand\mathstyle might not work correctly\@gobble}%
  \else
    \PackageWarning\bxluy@pkgname{%
      Ustackifying process failed\@gobble}%
  \fi\fi}

%--------------------------------------- all done
\endinput
%% EOF