How does renewcommand immediately following a beginitemize prevent missing item error

The itemize list below works fine. However, if I attempt to move the

itemize

renewcommand*do[1]item #1.

outside of the itemize, it results in a

Something's wrong--perhaps a missing item

renewcommand*do[1]item #1.

renewcommand

documentclassarticle usepackageetoolbox newcommandCSVList listaddCSVLista listaddCSVListb listaddCSVListc renewcommand*do[1]item #1.% begindocument beginitemize renewcommand*do[1]item #1.% dolistloopCSVList% enditemize %% -------------------- This results in the "missing item" error. % beginitemize % dolistloopCSVList% % enditemize enddocument

do is used everywhere. You should redefine it only very locally.

– Ulrike Fischer
Sep 12 '18 at 22:12

Avoid dolistloop and prefer forlistloop, where you specify a handler.

– egreg
Sep 12 '18 at 22:14

dolistloop

forlistloop

2 Answers
2

Because do is used at the begindocument by the LaTeX kernel to make the @onlypreamble commands throw an error when used outside the preamble.

do

begindocument

@onlypreamble

The definition of document contains:

document

gdefdo##1globallet ##1@notprerr% @preamblecmds globallet @nodocument relax globalletdonoexpand % <-- this causes the problem

so do becomes noexpand right after begindocument, so your newcommand in the preamble has no effect.

do

noexpand

begindocument

newcommand

If you put the renewcommand inside the itemize, when the environment group ends, the previous definition of do (noexpand) is restored and this raises the missing item.

renewcommand

itemize

do

noexpand

missing item

If you move the renewcommand outside the itemize, its new definition is kept until the second itemize and everything works fine.

renewcommand

itemize

Try this:

documentclassarticle usepackageetoolbox newcommandCSVList listaddCSVLista listaddCSVListb listaddCSVListc renewcommand*do[1]item #1.% begindocument beginitemize renewcommand*do[1]item #1.% dolistloopCSVList% enditemize beginitemize showdo dolistloopCSVList% enditemize enddocument

The console will show

> do=noexpand. l.18 showdo

Thus your doa will do

doa

noexpanditem a

and the output will be, after the “missing item” error, just

item

abc

Much better is to define a specific handler:

documentclassarticle usepackageetoolbox newcommandCSVList listaddCSVLista listaddCSVListb listaddCSVListc newcommand*doCSV[1]item #1. begindocument beginitemize forlistloopdoCSVCSVList enditemize enddocument

^{I have removed all superfluous % characters.}

%

A different implementation, where the handler is built on the fly; the current item in the list is denoted by #1.

#1

documentclassarticle usepackagexparse ExplSyntaxOn NewDocumentCommandaddtolistmm clist_if_exist:cF l_grill_list_#1_clist clist_new:c l_grill_list_#1_clist clist_map_inline:nn #2 clist_put_right:cn l_grill_list_#1_clist ##1 NewDocumentCommanduselistmm cs_set_protected:Nn __grill_uselist:n #2 clist_map_function:cN l_grill_list_#1_clist __grill_uselist:n ExplSyntaxOff addtolistCSVLista addtolistCSVListb,c begindocument beginitemize uselistCSVListitem #1. enditemize enddocument

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