% language=us

% TAKE FROM LOWLEVEL-EXPANSION.TEX

\usemodule[system-tokens]

\usemodule[present-boring,abbreviations-logos]

\definehighlight[nb][style=bold,color=middlegray,define=no]

\startdocument
  [title={PROGRAMMING},
   banner={local control},
   location={context\enspace {\bf 2021}\enspace meeting}]

\starttitle[title=Expansion]

\TEX\ can be in several so called input reading modes:

Users mostly see it reading from the source file(s). Characters are picked up and
interpreted. Depending on what token it becomes some action takes place.

\starttyping
1 \setbox0\hbox to 10pt{2} \count0=3 \the\count0 \multiply\count0 by 4
\stoptyping

\startitemize

\startitem
    The \type {1} gets typeset because characters like that are seen as text.
\stopitem

\startitem
    The \type {\setbox} primitive triggers picking up a register number, then
    goes on scanning for a box specification and that itself will typeset a
    sequence of whatever until the group ends.
\stopitem

\startitem
    The \type {count} primitive triggers scanning for a register number (or
    reference) and then scans for a number; the equal sign is optional.
\stopitem

\startitem
    The \type {the} primitive injects some value into the current input stream
    (it does so by entering a new input level).
\stopitem

\startitem
    The \type {multiply} primitive picks up a register specification and
    multiplies that by the next scanned number. The \type {by} is optional.
\stopitem

\startitem
    Printing from \LUA\ and scanning tokens with e.g.\ \type {\scantokens} is like
    reading (pseudo) files.
\stopitem

\stopitemize

\stoptitle

\starttitle[title=Expansion]

\startbuffer[def]
\def\TestA {1 \setbox0\hbox{2} \count0=3 \the\count0}
\stopbuffer

\startbuffer[edef]
\edef\TestB{1 \setbox0\hbox{2} \count0=3 \the\count0}
\stopbuffer

\typebuffer[def]
\typebuffer[edef]

\getbuffer[def]
\getbuffer[edef]

\blank[2*big]

\startcolumns[n=2] \switchtobodyfont[8pt]
\luatokentable\TestA
\column
\luatokentable\TestB
\stopcolumns

\stoptitle

\starttitle[title=Local control]

\startbuffer[edef]
\edef\TestB{1 \setbox0\hbox{2} \count0=3 \the\count0}
\stopbuffer

\startbuffer[ldef]
\edef\TestC{1 \setbox0\hbox{2} \localcontrolled{\count0=3} \the\count0}
\stopbuffer

\typebuffer[edef]
\typebuffer[ldef]

\getbuffer[edef]
\getbuffer[ldef]

\blank[2*big]

\startcolumns[n=2] \switchtobodyfont[8pt]
\luatokentable\TestB
\column
\luatokentable\TestC
\stopcolumns

\stoptitle

\starttitle[title=Side effects]

\startbuffer[edef]
\edef\TestB{1 \setbox0\hbox{2} \count0=3 \the\count0}
\stopbuffer

\startbuffer[ldef]
\edef\TestD{\localcontrolled{1 \setbox0\hbox{2} \count0=3 \the\count0}}
\stopbuffer

\typebuffer[edef]
\typebuffer[ldef]

\getbuffer[edef]\getbuffer[ldef]\quad{\darkgray\leftarrow\space Watch how the results end up here!}

\blank[2*big]

\startcolumns[n=2] \switchtobodyfont[8pt]
\luatokentable\TestB
\column
\luatokentable\TestD
\stopcolumns

\stoptitle

\starttitle[title=Usage]

\startbuffer[def]
\def\WidthOf#1%
  {\beginlocalcontrol
   \setbox0\hbox{#1}%
   \endlocalcontrol
   \wd0 }
\stopbuffer

\startbuffer[use]
\scratchdimen\WidthOf{The Rite Of Spring}

\the\scratchdimen
\stopbuffer

\typebuffer[def]
\typebuffer[use]

\getbuffer[def]\getbuffer[use]

\stoptitle

\starttitle[title=Not always pretty]

\startbuffer[def]
\def\WidthOf#1%
  {\dimexpr
      \beginlocalcontrol
        \begingroup
          \setbox0\hbox{#1}%
          \expandafter
        \endgroup
      \expandafter
      \endlocalcontrol
      \the\wd0
   \relax}
\stopbuffer

\startbuffer[use]
\scratchdimen\WidthOf{The Rite Of Spring}

\the\scratchdimen
\stopbuffer

\typebuffer[def]
\typebuffer[use]

\getbuffer[def]\getbuffer[use]

\stoptitle

\starttitle[title=The \LUA\ end]

Right from the start the way to get something into \TEX\ from \LUA\ has been the
print functions. But we can also go local (immediate). There are several methods:

\startitemize
\startitem via a set token register \stopitem
\startitem via a defined macro \stopitem
\startitem via a string \stopitem
\stopitemize

Among the things to keep in mind are catcodes, scope and expansion (especially in
when the result itself ends up in macros).

\stoptitle

\starttitle[title=Via a token register]

% runlocal : macro|toks expand group

\startbuffer[set]
\toks0={\setbox0\hbox{The Rite Of Spring (Igor Stravinsky)}}
\toks2={\setbox0\hbox{The Rite Of Spring (Joe Parrish)}}
\stopbuffer

\typebuffer[set]

\startbuffer[run]
\startluacode
tex.runlocal(0) context("[1: %p]",tex.box[0].width)
tex.runlocal(2) context("[2: %p]",tex.box[0].width)
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[set,run] \stop

\stoptitle

\starttitle[title=Via a token macro]

\startbuffer[set]
\def\TestA{\setbox0\hbox{The Rite Of Spring (Igor Stravinsky)}}
\def\TestB{\setbox0\hbox{The Rite Of Spring (Joe Parrish)}}
\stopbuffer

\typebuffer[set]

\startbuffer[run]
\startluacode
tex.runlocal("TestA") context("[3: %p]",tex.box[0].width)
tex.runlocal("TestB") context("[4: %p]",tex.box[0].width)
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[set,run] \stop

\stoptitle

\starttitle[title=Via a string]

\startbuffer[run]
\startluacode
tex.runstring([[\setbox0\hbox{The Rite Of Spring (Igor Stravinsky)}]])

context("[5: %p]",tex.box[0].width)

tex.runstring([[\setbox0\hbox{The Rite Of Spring (Joe Parrish)}]])

context("[6: %p]",tex.box[0].width)
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[run] \stop

\blank[2*big]

A bit more high level:

\starttyping
context.runstring([[\setbox0\hbox{(Here \bf 1.2345)}]])
context.runstring([[\setbox0\hbox{(Here \bf   %.3f)}]],1.2345)
\stoptyping

\stoptitle

\starttitle[title=Locked in \LUA]

\startbuffer[run]
\startluacode
token.setmacro("TestX",[[\setbox0\hbox{The Rite Of Spring (Igor)}]])
tex.runlocal("TestX")
context("[7: %p]",tex.box[0].width)
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[run] \stop

\startbuffer[run]
\startluacode
tex.scantoks(0,tex.ctxcatcodes,[[\setbox0\hbox{The Rite Of Spring (Joe)}]])
tex.runlocal(0)
context("[8: %p]",tex.box[0].width)
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[run] \stop

\stoptitle

\starttitle[title=Order matters]

A lot this relates to pushing stuff into the input which is stacked. Compare:

\startbuffer[run]
\startluacode
context("[HERE 1]")
context("[HERE 2]")
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[run] \stop

with this:

\startbuffer[run]
\startluacode
tex.pushlocal() context("[HERE 1]") tex.poplocal()
tex.pushlocal() context("[HERE 2]") tex.poplocal()
\stopluacode
\stopbuffer

\typebuffer[run]

\start \getbuffer[run] \stop

% \startluacode
% tex.runlocal(function() context("[Here 1]") end)
% context("[Here 12]")
% tex.runlocal(function() context("[Here 2]") end)
% \stopluacode

% tex.pushlocal % swaps order
% tex.poplocal
% tex.quitlocal

% token.expandmacro

% str   : serialized
% true  : wrap next {}
% table : {serialzed} {serialzed} {serialzed}
% token : inject
% number: catcode table

% tex.expandasvalue:
%     (kind, like expand_macro)

% tex.runstring:
%  [catcode] string expand grouped

% tex.runlocal
%     function|number(register)|string(macro)|userdata(token) / expand / grouped

% mplib.expandtex
%     mpx, kind, macro, arguments

\stopdocument