Cfrgtkky

I want to pass an argument to a self-made tabular environment in the following format:

begin{customTabular}{|c|c|}{'@'}

...such that the second argument (here '@', WITHIN PARANTHESIS) is treated as a column separator symbol by the LaTeX document. How this can be done? Please suggest the changes/modifications in the code attached.

The code for customTabular environment is as follows (here, mytabular is similar to customTabular):

usepackage{xparse}



ExplSyntaxOn

NewDocumentEnvironment {mytabular} { O{,} }

  {

    char_set_catcode_other:N &

    char_set_catcode_alignment:n {`#1}

    begin{tabular}

  }

  {

    end{tabular}

  }

ExplSyntaxOff

You need to make the argument an optional group (or perhaps mandatory), and to arrange to strip any quote marks before using as a number:

documentclass{article}

usepackage{xparse}

ExplSyntaxOn

NewDocumentEnvironment {mytabular} { O{c} m G{','} }

  {

    char_set_catcode_other:N &

    char_set_catcode_alignment:n { __mytab_test:n {#3} }

    begin{tabular}[#1]{#2}

  }

  {

    end{tabular}

  }

cs_new:Npn __mytab_test:n #1 { __mytab_test:w #1 ' #1 '' q_stop }

cs_new:Npn __mytab_test:w #1 ' #2 ' #3 q_stop { `#2 }

ExplSyntaxOff



begin{document}

begin{mytabular}{cc}{'@'}

  a @ b\

  c @ d

end{mytabular}



begin{mytabular}{cc}{@}

  a @ b\

  c @ d

end{mytabular}

end{document}

The trick in removing ' tokens is that TeX is greedy in a match. So with

#1 ' #2 ' #3

any input containing a leading ' will have an empty #1, the 'argument' in #2 and rubbish left in #3. If there was no leading ', then #1 will be the same as #2 due to the set up macro, which supplies the input both with and without additional ' tokens.

If you don't require the quotes, your code works, provided you use square brackets for the argument. It's better style to also add the mandatory argument for the columns.

documentclass{article}

usepackage{xparse}



ExplSyntaxOn

NewDocumentEnvironment {mytabular} { O{,} m }

  {

    char_set_catcode_other:N &

    char_set_catcode_alignment:n {`#1}

    begin{tabular}{#2}

  }

  {

    end{tabular}

  }

ExplSyntaxOff



begin{document}



begin{mytabular}[@]{cc}

  a @ b\

  c @ d

end{mytabular}



begin{mytabular}{cc}

  a , b\

  c , d

end{mytabular}



end{document}

If you want a syntax such as begin{mytabular}{cc}[@], just exchange the arguments

NewDocumentEnvironment {mytabular} { m O{,} }

  {

    char_set_catcode_other:N &

    char_set_catcode_alignment:n {`#2}

    begin{tabular}{#1}

  }

  {

    end{tabular}

  }