Etydhv

In order to simplify data entry with as little markup of the data as possible, I am attempting the following:

documentclassarticle

usepackageetoolbox

begingroup
 obeylines
 gdefing#1 #2 #3gapptotabbody% Collect rows of tabular[x] in tabbody
 %% Ignore #1 and/or #2 if empty (= . )
 if.#2
 if.#1
 &&#3\
 else
 #1&&#3\
 fi
 else
 if.#1
 &#2&#3\
 else
 #1&#2&#3\
 fi
 fi
 %

endgroup

%%%%%% This, without the if's works, though it does not do what I need:

begingroup
obeylines
gdefiing#1 #2 #3gapptotabbody% Collect rows of tabular[x] in tabbody
 #1&#2&#3\
 %

endgroup

begindocument

begingroup
obeylines
everypar=ing %<<<--- change to iing and there is no error
a 1 u
b 2 v
. 3 w
d 4 x
e 5 y
f 6 z
endgroup

begintabularccc
 tabbody
endtabular

enddocument

I'm getting an unexpected error:

ERROR: Incomplete if; all text was ignored after line 39.

--- TeX said ---
<inserted text> 
 fi 
l.39 ^^I^^Itabbody

I have looked at past queries, but have not thus far found an answer. If I remove all of the if statements from the definition of ing (=iing) the problem goes a way. Quite sure I'm missing something really basic -- something to do with the timing of the expansion of the ifs, but I'm stuck for the moment.

You don't want to define ing under the scope of obeylines, but just use the active ^^M as delimiter (reinserting it at the end so a par will be issued.

You also want to expand the conditionals before appending the result to tabbody.

documentclassarticle
usepackageetoolbox

begingrouplccode`~=`^^Mlowercaseendgroupdefing#1 #2 #3~%
 xapptotabbody% Collect rows of tabular[x] in tabbody
 %% Ignore #1 and/or #2 if empty (= . )
 if.#2%
 if.#1%
 unexpanded&&#3\%
 else
 unexpanded#1&&#3\%
 fi
 else
 if.#1%
 unexpanded&#2&#3\%
 else
 unexpanded#1&#2&#3\%
 fi
 fi
 ~% we want a `par`


begindocument

begingroup
obeylines
everypar=ing %<<<--- change to iing and there is no error
a 1 u
b 2 v
. 3 w
d 4 x
e 5 y
f 6 z
endgroup

%showtabbody % for debugging

begintabularccc
 tabbody
endtabular

enddocument