that's a complicated grammar

> Can someone help me get started

you can regex it to become Perl code of nested calls and eval it

like

        -tex_args 
            -sub_args +debug_dir=./ 
            -sub_args +debug_dir=./ 
        -tex_args-
[download]

becoming

minus::tex_args 
    minus::sub_args plus::debug_dir '=./' , 
        minus::sub_args plus::debug_dir '=./' , 
            minus::tex_args '-'
[download]

now you can populate the packages minus and plus with appropriate functions dealing with the input.

The subs are called from right to left.

start with all of the like sub text_args { return ["-text_args", @_] } and then you'll have a start to improve your grammar.