Tokenizing and parsing a word

Question

After a 10+ year LaTeX hiatus I am returning and slowly getting hold again of macro writing.

I now want to parse a string like "fisis" into the first letter "f" and the second half "isis". Case sensitivity is not really an issue.

Valid tokens obey the following rules:

1. The first letter must be one of {a, b, c..., g}
2. The second part of the token consists of exactly 0, 1 or 2 times the token "es" or "is"

For example, "cesis" is invalid as "es" cannot be followed by "is" according to rule 2.

The use case is creating a multi-lingual rendering of the tonality of a musical piece via a macro, e.g.: \tonality{fis}{minor} which would be rendered in German, French and English as follows: {Fis-moll. {\emph Fa dièse mineur.} F sharp minor.}

E.g., the first example "fisis" would be parsed as ( "f"; "is" x 2 ) which would be rendered as "F double sharp" in English (with the \tonalityEN macro) and "Ré double dièse" in French (with the \tonalityFR macro).

How can this be achieved?

Answer 1

I don't completely get your question but the following can perform some tests and can be build upon if you can describe how to handle the language switches. I've used the convenient xstring which comes with quite powerful string handling tools as sampled below. First we remove the initial character and then test if the rest of the word has the first two chars of the remaining part. If there is something left out after deleting the detected two-letter it gives an error. After that it's straightforward.

\documentclass{article}
\usepackage{xstring}
\def\parsethis#1{%
\if\relax#1\relax\else%
\StrLeft{#1}{1}[\myfirstletter]
\StrGobbleLeft{#1}{1}[\myrestofword]
\StrLeft{\myrestofword}{2}[\mysample]
\StrCount{\myrestofword}{\mysample}[\numofreps]
\StrDel{\myrestofword}{\mysample}[\remainingchars]
\if\relax\remainingchars\relax%
I found \numofreps\space copies of the string ``\mysample''.%
\else
There is a mixture of es and is.%
\fi
}

\begin{document}
\parsethis{cisis}\par
\parsethis{feseses}\par
\parsethis{dadadadad}\par
\parsethis{b}\par
\parsethis{basis}
\end{document}

Answer 2

You can possibly check whether the new LaTeX3 programming style suits you:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand { \tonality } { m m }
 {
  \ton_tonality:nn { #1 } { #2 }
 }

\tl_new:N \l_ton_key_tl
\tl_new:N \l_ton_accidents_tl
\cs_new_protected:Npn \ton_tonality:nn #1 #2
 {
  % Normalize to uppercase
  \tl_to_uppercase:n
   {
    % Get the key
    \tl_set:Nx \l_ton_key_tl { \tl_head:n { #1 } }
    % Get the accidents
    \tl_set:Nx \l_ton_accidents_tl { \tl_tail:n { #1 } }
   }
  % check the key
  \str_case:onn { \l_ton_key_tl }
   {
    {A}{ \ton_print_key:n {A} }
    {B}{ \ton_print_key:n {B} }
    {C}{ \ton_print_key:n {C} }
    {D}{ \ton_print_key:n {D} }
    {E}{ \ton_print_key:n {E} }
    {F}{ \ton_print_key:n {F} }
    {G}{ \ton_print_key:n {G} }
   }
   { \msg_error:nn { tonality } { bad-key } !! }
  % check the accidents
  \str_case:onn { \l_ton_accidents_tl }
   {
    {}    { }
    {ES}  { \ton_print_flat: }
    {ESES}{ \ton_print_doubleflat: }
    {IS}  { \ton_print_sharp: }
    {ISIS}{ \ton_print_doublesharp: }
   }
   { \msg_error:nn { tonality } { bad-accidents } !! }
  \ton_print_mode:n { #2 }
 }

\cs_new:Npn \ton_print_mode:n #1 { \nobreakspace #1 }

\cs_new:Npn \ton_print_key:n #1 { #1 }
\cs_new:Npn \ton_print_flat: { \nobreakspace flat }
\cs_new:Npn \ton_print_doubleflat: { \nobreakspace doubleflat }
\cs_new:Npn \ton_print_sharp: { \nobreakspace sharp }
\cs_new:Npn \ton_print_doublesharp: {\nobreakspace doublesharp }

\msg_new:nnnn { tonality } { bad-key }
 { Key~not~in~range~A--G }
 { The~first~character~is~not~good }
\msg_new:nnnn { tonality } { bad-accidents }
 { Bad~accidents~specification }
 { The~string~for~the~accidents~is~wrong }

\ExplSyntaxOff

\begin{document}
\tonality{A}{minor}

\tonality{fis}{minor}

\tonality{fesis}{major}

\tonality{qisis}{major}
\end{document}

Answer 3

This example is plain tex but would work in latex of course.

\def\zz#1{%
\edef\tmp{\noexpand\zzformat
\zzz#1\relax\relax\relax\relax\relax\relax}%
%show\tmp
\tmp}

\def\zzz#1#2#3#4#5#6#7{%
{#1}%
\ifx\relax#2{0}{}%
\else\ifx\relax#4{1}{#2#3}%
\else{2}{#2#3}\fi\fi}

\def\zzformat#1#2#3{%
#1 + #2 ( #3 )
}

\zz{a}

\zz{aes}

\zz{fisis}

\bye

Answer 4

I managed to find a solution thanks to your input. Below you'll find a documented debug version - I hope it will be useful to others.

\documentclass{article}
\usepackage{xstring}

\def\flatmodifier{es}
\def\sharpmodifier{is}
\def\naturalmodifier{}

\parindent 0cm

\def\parsethis#1{%
    {\bf{#1}\par}%
    \if\relax#1\relax\else%
    \StrLeft{#1}{1}[\myfirstletter]%                            \myfirstletter = root tone
    \StrPosition{abcdefg}{\myfirstletter}[\mynote]
    \ifnum\mynote=0%
        ERROR!!! Invalid note name (\myfirstletter)\par
    \else
        \StrGobbleLeft{#1}{1}[\myrestofword]%                       Eat first letter
        \StrLeft{\myrestofword}{2}[\mysample]%                      \mysample = 2 characters after the root tone
        \ifx\mysample\naturalmodifier%                                      (Natural)
            \def\mytonemodifier{Natural}%
        \else
            \ifx\mysample\flatmodifier%                                     (Flat)
                    \def\mytonemodifier{Flat}%
            \else
                \ifx\mysample\sharpmodifier%                                (Sharp)
                    \def\mytonemodifier{Sharp}%
                \else
                    \def\mytonemodifier{\relax}%                    (Invalid)
                \fi
            \fi
        \fi
        \if\mytonemodifier\relax
            ERROR!!! Invalid note pitch modifier (\mysample)\par
        \else
            Okay, we can proceed.\par
            \StrCount{\myrestofword}{\mysample}[\numofreps]%            \numofreps = # repetitions of \mysample
            \StrDel{\myrestofword}{\mysample}[\remainingchars]%         \remainingchars = remaining characters after removing \mysample from the front
            \if\relax\remainingchars\relax%                                 IF there are remaining characters
                {\small I found \numofreps\space copies of the string ``\mysample''.\par}%
                \ifnum\numofreps<3%
                    \myfirstletter\ %                                           Display note name
                    \ifnum\numofreps=0%                                         No modifier
                        \mytonemodifier\ %                                          Display note modifier
                    \else
                        \ifnum\numofreps=2%                                         Double flat/sharp
                            Double %
                        \fi
                        \mytonemodifier\ %                                          Display note modifier
                    \fi
                \else%                                                          ELSE
                    ERROR: Too many accidental modifiers (\numofreps).%
                \fi%                                                            ENDIF
            \else
                ERROR: There is a mixture of es and is.%
            \fi
        \fi
    \fi
}

\begin{document}
\parsethis{h}\par
\parsethis{b}\par
\parsethis{be}\par
\parsethis{bas}\par
\parsethis{bes}\par
\parsethis{bese}\par
\parsethis{beses}\par
\parsethis{cisis}\par
\parsethis{feseses}\par
\parsethis{fesesis}\par
\parsethis{dadadadad}\par
\parsethis{basis}\par
\parsethis{benhottentottententententoonstelling}\par
\end{document}