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l3str.dtx
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l3str.dtx
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% \iffalse meta-comment
%
%% File: l3str.dtx
%
% Copyright (C) 2011-2022 The LaTeX Project
%
% It may be distributed and/or modified under the conditions of the
% LaTeX Project Public License (LPPL), either version 1.3c of this
% license or (at your option) any later version. The latest version
% of this license is in the file
%
% https://www.latex-project.org/lppl.txt
%
% This file is part of the "l3kernel bundle" (The Work in LPPL)
% and all files in that bundle must be distributed together.
%
% -----------------------------------------------------------------------
%
% The development version of the bundle can be found at
%
% https://github.com/latex3/latex3
%
% for those people who are interested.
%
%<*driver>
\documentclass[full,kernel]{l3doc}
\begin{document}
\DocInput{\jobname.dtx}
\end{document}
%</driver>
% \fi
%
% \title{^^A
% The \pkg{l3str} package: Strings^^A
% }
%
% \author{^^A
% The \LaTeX{} Project\thanks
% {^^A
% E-mail:
% \href{mailto:latex-team@latex-project.org}
% {latex-team@latex-project.org}^^A
% }^^A
% }
%
% \date{Released 2022-09-28}
%
% \maketitle
%
% \begin{documentation}
%
% \TeX{} associates each character with a category code: as such, there is no
% concept of a \enquote{string} as commonly understood in many other
% programming languages. However, there are places where we wish to manipulate
% token lists while in some sense \enquote{ignoring} category codes: this is
% done by treating token lists as strings in a \TeX{} sense.
%
% A \TeX{} string (and thus an \pkg{expl3} string) is a series of characters
% which have category code $12$ (\enquote{other}) with the exception of
% space characters which have category code $10$ (\enquote{space}). Thus
% at a technical level, a \TeX{} string is a token list with the appropriate
% category codes. In this documentation, these are simply referred to as
% strings.
%
% String variables are simply specialised token lists, but by convention
% should be named with the suffix \texttt{\ldots{}str}. Such variables
% should contain characters with category code $12$ (other), except
% spaces, which have category code $10$ (blank space). All the
% functions in this module which accept a token list argument first
% convert it to a string using \cs{tl_to_str:n} for internal processing,
% and do not treat a token list or the corresponding string
% representation differently.
%
% As a string is a subset of the more general token list, it is sometimes unclear
% when one should be used over the other.
% Use a string variable for data that isn't primarily intended for typesetting
% and for which a level of protection from unwanted expansion is suitable.
% This data type simplifies comparison of variables since there are no concerns
% about expansion of their contents.
%
% The functions \cs{cs_to_str:N}, \cs{tl_to_str:n}, \cs{tl_to_str:N} and
% \cs{token_to_str:N} (and variants) generate strings from the appropriate
% input: these are documented in \pkg{l3basics}, \pkg{l3tl} and \pkg{l3token},
% respectively.
%
% Most expandable functions in this module come in three flavours:
% \begin{itemize}
% \item \cs[no-index]{str_\ldots{}:N}, which expect a token list or string
% variable as their argument;
% \item \cs[no-index]{str_\ldots{}:n}, taking any token list (or string) as an
% argument;
% \item \cs[no-index]{str_\ldots{}_ignore_spaces:n}, which ignores any space
% encountered during the operation: these functions are typically
% faster than those which take care of escaping spaces
% appropriately.
% \end{itemize}
%
% \section{Creating and initialising string variables}
%
% \begin{function}[added = 2015-09-18]{\str_new:N, \str_new:c}
% \begin{syntax}
% \cs{str_new:N} \meta{str~var}
% \end{syntax}
% Creates a new \meta{str~var} or raises an error if the name is
% already taken. The declaration is global. The \meta{str~var} is
% initially empty.
% \end{function}
%
% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
% {
% \str_const:Nn, \str_const:NV, \str_const:Nx,
% \str_const:cn, \str_const:cV, \str_const:cx
% }
% \begin{syntax}
% \cs{str_const:Nn} \meta{str~var} \Arg{token list}
% \end{syntax}
% Creates a new constant \meta{str~var} or raises an error if the name
% is already taken. The value of the \meta{str~var} is set
% globally to the \meta{token list}, converted to a string.
% \end{function}
%
% \begin{function}[added = 2015-09-18]
% {\str_clear:N, \str_clear:c, \str_gclear:N, \str_gclear:c}
% \begin{syntax}
% \cs{str_clear:N} \meta{str~var}
% \end{syntax}
% Clears the content of the \meta{str~var}.
% \end{function}
%
% \begin{function}[added = 2015-09-18]{\str_clear_new:N, \str_clear_new:c}
% \begin{syntax}
% \cs{str_clear_new:N} \meta{str~var}
% \end{syntax}
% Ensures that the \meta{str~var} exists globally by applying
% \cs{str_new:N} if necessary, then applies
% \cs[index=str_clear:N]{str_(g)clear:N} to leave
% the \meta{str~var} empty.
% \end{function}
%
% \begin{function}[added = 2015-09-18]
% {
% \str_set_eq:NN, \str_set_eq:cN, \str_set_eq:Nc, \str_set_eq:cc,
% \str_gset_eq:NN, \str_gset_eq:cN, \str_gset_eq:Nc, \str_gset_eq:cc
% }
% \begin{syntax}
% \cs{str_set_eq:NN} \meta{str~var_1} \meta{str~var_2}
% \end{syntax}
% Sets the content of \meta{str~var_1} equal to that of
% \meta{str~var_2}.
% \end{function}
%
% \begin{function}[added = 2017-10-08]
% {
% \str_concat:NNN, \str_concat:ccc,
% \str_gconcat:NNN, \str_gconcat:ccc
% }
% \begin{syntax}
% \cs{str_concat:NNN} \meta{str~var_1} \meta{str~var_2} \meta{str~var_3}
% \end{syntax}
% Concatenates the content of \meta{str~var_2} and \meta{str~var_3}
% together and saves the result in \meta{str~var_1}. The \meta{str~var_2}
% is placed at the left side of the new string variable.
% The \meta{str~var_2} and \meta{str~var_3} must indeed be strings, as
% this function does not convert their contents to a string.
% \end{function}
%
% \begin{function}[EXP, pTF, added = 2015-09-18]
% {\str_if_exist:N, \str_if_exist:c}
% \begin{syntax}
% \cs{str_if_exist_p:N} \meta{str~var}
% \cs{str_if_exist:NTF} \meta{str~var} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests whether the \meta{str~var} is currently defined. This does not
% check that the \meta{str~var} really is a string.
% \end{function}
%
% \section{Adding data to string variables}
%
% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
% {
% \str_set:Nn, \str_set:NV, \str_set:Nx,
% \str_set:cn, \str_set:cV, \str_set:cx,
% \str_gset:Nn, \str_gset:NV, \str_gset:Nx,
% \str_gset:cn, \str_gset:cV, \str_gset:cx
% }
% \begin{syntax}
% \cs{str_set:Nn} \meta{str var} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string}, and stores the
% result in \meta{str var}.
% \end{function}
%
% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
% {
% \str_put_left:Nn, \str_put_left:NV, \str_put_left:Nx,
% \str_put_left:cn, \str_put_left:cV, \str_put_left:cx,
% \str_gput_left:Nn, \str_gput_left:NV, \str_gput_left:Nx,
% \str_gput_left:cn, \str_gput_left:cV, \str_gput_left:cx
% }
% \begin{syntax}
% \cs{str_put_left:Nn} \meta{str var} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string}, and prepends the
% result to \meta{str var}. The current contents of the \meta{str
% var} are not automatically converted to a string.
% \end{function}
%
% \begin{function}[added = 2015-09-18, updated = 2018-07-28]
% {
% \str_put_right:Nn, \str_put_right:NV, \str_put_right:Nx,
% \str_put_right:cn, \str_put_right:cV, \str_put_right:cx,
% \str_gput_right:Nn, \str_gput_right:NV, \str_gput_right:Nx,
% \str_gput_right:cn, \str_gput_right:cV, \str_gput_right:cx
% }
% \begin{syntax}
% \cs{str_put_right:Nn} \meta{str var} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string}, and appends the
% result to \meta{str var}. The current contents of the \meta{str
% var} are not automatically converted to a string.
% \end{function}
%
% \section{String conditionals}
%
% \begin{function}[EXP,pTF, added = 2015-09-18, updated = 2022-03-21]
% {\str_if_empty:N, \str_if_empty:c, \str_if_empty:n}
% \begin{syntax}
% \cs{str_if_empty_p:N} \meta{str~var}
% \cs{str_if_empty:NTF} \meta{str~var} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests if the \meta{string variable} is entirely empty
% (\emph{i.e.}~contains no characters at all).
% \end{function}
%
% \begin{function}[EXP,pTF, added = 2015-09-18]
% {\str_if_eq:NN, \str_if_eq:Nc, \str_if_eq:cN, \str_if_eq:cc}
% \begin{syntax}
% \cs{str_if_eq_p:NN} \meta{str~var_1} \meta{str~var_2}
% \cs{str_if_eq:NNTF} \meta{str~var_1} \meta{str~var_2} \Arg{true code} \Arg{false code}
% \end{syntax}
% Compares the content of two \meta{str variables} and
% is logically \texttt{true} if the two contain the same characters
% in the same order. See \cs{tl_if_eq:NNTF} to compare tokens
% (including their category codes) rather than characters.
% \end{function}
%
% \begin{function}[EXP,pTF, updated = 2018-06-18]
% {
% \str_if_eq:nn, \str_if_eq:Vn, \str_if_eq:on, \str_if_eq:no,
% \str_if_eq:nV, \str_if_eq:VV, \str_if_eq:vn, \str_if_eq:nv,
% \str_if_eq:ee
% }
% \begin{syntax}
% \cs{str_if_eq_p:nn} \Arg{tl_1} \Arg{tl_2}
% \cs{str_if_eq:nnTF} \Arg{tl_1} \Arg{tl_2} \Arg{true code} \Arg{false code}
% \end{syntax}
% Compares the two \meta{token lists} on a character by character
% basis (namely after converting them to strings),
% and is \texttt{true} if the two \meta{strings} contain the same
% characters in the same order. Thus for example
% \begin{verbatim}
% \str_if_eq_p:no { abc } { \tl_to_str:n { abc } }
% \end{verbatim}
% is logically \texttt{true}. See \cs{tl_if_eq:nnTF} to compare
% tokens (including their category codes) rather than characters.
% \end{function}
%
% \begin{function}[TF, added = 2017-10-08]{\str_if_in:Nn, \str_if_in:cn}
% \begin{syntax}
% \cs{str_if_in:NnTF} \meta{str~var} \Arg{token list} \Arg{true code} \Arg{false code}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} and
% tests if that \meta{string} is found in the content of the
% \meta{str~var}.
% \end{function}
%
% \begin{function}[TF, added = 2017-10-08]{\str_if_in:nn}
% \begin{syntax}
% \cs{str_if_in:nnTF} \Arg{tl_1} \Arg{tl_2} \Arg{true code} \Arg{false code}
% \end{syntax}
% Converts both \meta{token lists} to \meta{strings} and
% tests whether \meta{string_2} is found inside \meta{string_1}.
% \end{function}
%
% \begin{function}[added = 2013-07-24, updated = 2022-03-21, EXP, noTF]
% {\str_case:nn, \str_case:Vn, \str_case:Nn, \str_case:on, \str_case:nV, \str_case:nv}
% \begin{syntax}
% \cs{str_case:nnTF} \Arg{test string} \\
% ~~|{| \\
% ~~~~\Arg{string case_1} \Arg{code case_1} \\
% ~~~~\Arg{string case_2} \Arg{code case_2} \\
% ~~~~\ldots \\
% ~~~~\Arg{string case_n} \Arg{code case_n} \\
% ~~|}| \\
% ~~\Arg{true code}
% ~~\Arg{false code}
% \end{syntax}
% Compares the \meta{test string} in turn with each
% of the \meta{string cases} (all token lists are converted to strings).
% If the two are equal (as described for
% \cs{str_if_eq:nnTF}) then the associated \meta{code} is left in the
% input stream and other cases are discarded. If any of the
% cases are matched, the \meta{true code} is also inserted into the
% input stream (after the code for the appropriate case), while if none
% match then the \meta{false code} is inserted. The function
% \cs{str_case:nn}, which does nothing if there is no match, is also
% available.
%
% This set of functions performs no expansion on each
% \meta{string~case} argument, so any variable in there will be
% compared as a string. If expansion is needed in the
% \meta{string~cases}, then \cs[no-index]{str_case_e:nn(TF)} should
% be used instead.
% \end{function}
%
% \begin{function}[added = 2018-06-19, EXP, noTF]{\str_case_e:nn}
% \begin{syntax}
% \cs{str_case_e:nnTF} \Arg{test string} \\
% ~~|{| \\
% ~~~~\Arg{string case_1} \Arg{code case_1} \\
% ~~~~\Arg{string case_2} \Arg{code case_2} \\
% ~~~~\ldots \\
% ~~~~\Arg{string case_n} \Arg{code case_n} \\
% ~~|}| \\
% ~~\Arg{true code}
% ~~\Arg{false code}
% \end{syntax}
% Compares the full expansion of the \meta{test string}
% in turn with the full expansion of the \meta{string cases}
% (all token lists are converted to strings). If the two
% full expansions are equal (as described for \cs{str_if_eq:nnTF}) then the
% associated \meta{code} is left in the input stream
% and other cases are discarded. If any of the
% cases are matched, the \meta{true code} is also inserted into the
% input stream (after the code for the appropriate case), while if none
% match then the \meta{false code} is inserted. The function
% \cs{str_case_e:nn}, which does nothing if there is no match, is also
% available.
% The \meta{test string} is expanded in each comparison, and must
% always yield the same result: for example, random numbers must
% not be used within this string.
% \end{function}
%
% \begin{function}[EXP, pTF, added = 2021-05-17]{\str_compare:nNn, \str_compare:eNe}
% \begin{syntax}
% \cs{str_compare_p:nNn} \Arg{tl_1} \meta{relation} \Arg{tl_2}
% \cs{str_compare:nNnTF} \Arg{tl_1} \meta{relation} \Arg{tl_2} \Arg{true code} \Arg{false code}
% \end{syntax}
% Compares the two \meta{token lists} on a character by character
% basis (namely after converting them to strings) in a lexicographic
% order according to the character codes of the characters. The
% \meta{relation} can be |<|, |=|, or~|>| and the test is
% \texttt{true} under the following conditions:
% \begin{itemize}
% \item for |<|, if the first string is earlier than the second in lexicographic order;
% \item for |=|, if the two strings have exactly the same characters;
% \item for |>|, if the first string is later than the second in lexicographic order.
% \end{itemize}
% Thus for example the following is logically \texttt{true}:
% \begin{verbatim}
% \str_compare_p:nNn { ab } < { abc }
% \end{verbatim}
% \begin{texnote}
% This is a wrapper around the \TeX{} primitive
% \cs[index=pdfstrcmp]{(pdf)strcmp}. It is meant for programming
% and not for sorting textual contents, as it simply considers
% character codes and not more elaborate considerations of grapheme
% clusters, locale, etc.
% \end{texnote}
% \end{function}
%
% \section{Mapping over strings}
%
% All mappings are done at the current group level, \emph{i.e.}~any
% local assignments made by the \meta{function} or \meta{code} discussed
% below remain in effect after the loop.
%
% \begin{function}[added = 2017-11-14, rEXP]
% {\str_map_function:nN, \str_map_function:NN, \str_map_function:cN}
% \begin{syntax}
% \cs{str_map_function:nN} \Arg{token list} \meta{function}
% \cs{str_map_function:NN} \meta{str~var} \meta{function}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} then
% applies \meta{function} to every \meta{character} in the
% \meta{string} including spaces.
% \end{function}
%
% \begin{function}[added = 2017-11-14]
% {\str_map_inline:nn, \str_map_inline:Nn, \str_map_inline:cn}
% \begin{syntax}
% \cs{str_map_inline:nn} \Arg{token list} \Arg{inline function}
% \cs{str_map_inline:Nn} \meta{str~var} \Arg{inline function}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} then
% applies the \meta{inline function} to every \meta{character} in the
% \meta{str~var} including spaces.
% The \meta{inline function} should consist of code which
% receives the \meta{character} as |#1|.
% \end{function}
%
% \begin{function}[rEXP, added = 2021-05-05]
% {\str_map_tokens:nn, \str_map_tokens:Nn, \str_map_tokens:cn}
% \begin{syntax}
% \cs{str_map_tokens:nn} \Arg{token list} \Arg{code}
% \cs{str_map_tokens:Nn} \meta{str~var} \Arg{code}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} then applies
% \meta{code} to every \meta{character} in the \meta{string} including
% spaces. The \meta{code} receives each character as a trailing brace
% group. This is equivalent to \cs{str_map_function:nN} if the
% \meta{code} consists of a single function.
% \end{function}
%
% \begin{function}[added = 2017-11-14]
% {\str_map_variable:nNn, \str_map_variable:NNn, \str_map_variable:cNn}
% \begin{syntax}
% \cs{str_map_variable:nNn} \Arg{token list} \meta{variable} \Arg{code}
% \cs{str_map_variable:NNn} \meta{str~var} \meta{variable} \Arg{code}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} then stores each
% \meta{character} in the \meta{string} (including spaces) in turn in
% the (string or token list) \meta{variable} and applies the
% \meta{code}. The \meta{code} will usually make use of the
% \meta{variable}, but this is not enforced. The assignments to the
% \meta{variable} are local. Its value after the loop is the last
% \meta{character} in the \meta{string}, or its original value if the
% \meta{string} is empty. See also \cs{str_map_inline:Nn}.
% \end{function}
%
% \begin{function}[added = 2017-10-08, rEXP]{\str_map_break:}
% \begin{syntax}
% \cs{str_map_break:}
% \end{syntax}
% Used to terminate a \cs[no-index]{str_map_\ldots} function before all
% characters in the \meta{string} have been processed. This
% normally takes place within a conditional statement, for example
% \begin{verbatim}
% \str_map_inline:Nn \l_my_str
% {
% \str_if_eq:nnT { #1 } { bingo } { \str_map_break: }
% % Do something useful
% }
% \end{verbatim}
% See also \cs{str_map_break:n}.
% Use outside of a \cs[no-index]{str_map_\ldots} scenario leads to low
% level \TeX{} errors.
% \begin{texnote}
% When the mapping is broken, additional tokens may be inserted
% before continuing with the
% code that follows the loop.
% This depends on the design of the mapping function.
% \end{texnote}
% \end{function}
%
% \begin{function}[added = 2017-10-08, rEXP]{\str_map_break:n}
% \begin{syntax}
% \cs{str_map_break:n} \Arg{code}
% \end{syntax}
% Used to terminate a \cs[no-index]{str_map_\ldots} function before all
% characters in the \meta{string} have been processed, inserting
% the \meta{code} after the mapping has ended. This
% normally takes place within a conditional statement, for example
% \begin{verbatim}
% \str_map_inline:Nn \l_my_str
% {
% \str_if_eq:nnT { #1 } { bingo }
% { \str_map_break:n { <code> } }
% % Do something useful
% }
% \end{verbatim}
% Use outside of a \cs[no-index]{str_map_\ldots} scenario leads to low
% level \TeX{} errors.
% \begin{texnote}
% When the mapping is broken, additional tokens may be inserted
% before the \meta{code} is
% inserted into the input stream.
% This depends on the design of the mapping function.
% \end{texnote}
% \end{function}
%
% \section{Working with the content of strings}
%
% \begin{function}[EXP, added = 2015-09-18]{\str_use:N, \str_use:c}
% \begin{syntax}
% \cs{str_use:N} \meta{str~var}
% \end{syntax}
% Recovers the content of a \meta{str~var} and places it
% directly in the input stream. An error is raised if the variable
% does not exist or if it is invalid. Note that it is possible to use
% a \meta{str} directly without an accessor function.
% \end{function}
%
% \begin{function}[EXP, added = 2015-09-18]
% {\str_count:N, \str_count:c, \str_count:n, \str_count_ignore_spaces:n}
% \begin{syntax}
% \cs{str_count:n} \Arg{token list}
% \end{syntax}
% Leaves in the input stream the number of characters in the string
% representation of \meta{token list}, as an integer denotation. The
% functions differ in their treatment of spaces. In the case of
% \cs{str_count:N} and \cs{str_count:n}, all characters including
% spaces are counted. The \cs{str_count_ignore_spaces:n} function
% leaves the number of non-space characters in the input stream.
% \end{function}
%
% \begin{function}[EXP, added = 2015-09-18]
% {\str_count_spaces:N, \str_count_spaces:c, \str_count_spaces:n}
% \begin{syntax}
% \cs{str_count_spaces:n} \Arg{token list}
% \end{syntax}
% Leaves in the input stream the number of space characters in the
% string representation of \meta{token list}, as an integer
% denotation. Of course, this function has no \texttt{_ignore_spaces}
% variant.
% \end{function}
%
% \begin{function}[EXP, added = 2015-09-18]
% {\str_head:N, \str_head:c, \str_head:n, \str_head_ignore_spaces:n}
% \begin{syntax}
% \cs{str_head:n} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} into a \meta{string}. The first
% character in the \meta{string} is then left in the input stream,
% with category code \enquote{other}. The functions differ if the
% first character is a space: \cs{str_head:N} and \cs{str_head:n}
% return a space token with category code~$10$ (blank space), while
% the \cs{str_head_ignore_spaces:n} function ignores this space
% character and leaves the first non-space character in the input
% stream. If the \meta{string} is empty (or only contains spaces in
% the case of the \texttt{_ignore_spaces} function), then nothing is
% left on the input stream.
% \end{function}
%
% \begin{function}[EXP, added = 2015-09-18]
% {\str_tail:N, \str_tail:c, \str_tail:n, \str_tail_ignore_spaces:n}
% \begin{syntax}
% \cs{str_tail:n} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string}, removes the first
% character, and leaves the remaining characters (if any) in the input
% stream, with category codes $12$ and $10$ (for spaces). The
% functions differ in the case where the first character is a space:
% \cs{str_tail:N} and \cs{str_tail:n} only trim that space, while
% \cs{str_tail_ignore_spaces:n} removes the first non-space character
% and any space before it. If the \meta{token list} is empty (or
% blank in the case of the \texttt{_ignore_spaces} variant), then
% nothing is left on the input stream.
% \end{function}
%
% \begin{function}[EXP, added = 2015-09-18]
% {\str_item:Nn, \str_item:nn, \str_item_ignore_spaces:nn}
% \begin{syntax}
% \cs{str_item:nn} \Arg{token list} \Arg{integer expression}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string}, and leaves in the
% input stream the character in position \meta{integer expression} of
% the \meta{string}, starting at $1$ for the first (left-most)
% character. In the case of \cs{str_item:Nn} and \cs{str_item:nn},
% all characters including spaces are taken into account. The
% \cs{str_item_ignore_spaces:nn} function skips spaces when counting
% characters. If the \meta{integer expression} is negative,
% characters are counted from the end of the \meta{string}. Hence,
% $-1$ is the right-most character, \emph{etc.}
% \end{function}
%
% \begin{function}[EXP, added = 2015-09-18]
% {
% \str_range:Nnn, \str_range:cnn, \str_range:nnn,
% \str_range_ignore_spaces:nnn
% }
% \begin{syntax}
% \cs{str_range:nnn} \Arg{token list} \Arg{start index} \Arg{end index}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string}, and leaves in the
% input stream the characters from the \meta{start index} to the
% \meta{end index} inclusive. Spaces are preserved and counted as items
% (contrast this with \cs{tl_range:nnn} where spaces are not counted as
% items and are possibly discarded from the output).
%
% Here \meta{start index} and \meta{end index} should be integer denotations.
% For describing in detail the functions' behavior, let $m$ and $n$ be the start
% and end index respectively. If either is $0$, the result is empty. A positive
% index means `start counting from the left end', a negative index means
% `start counting from the right end'. Let $l$ be the count of the token list.
%
% The \emph{actual start point} is determined as $M=m$ if~$m>0$ and as $M=l+m+1$
% if~$m<0$. Similarly the \emph{actual end point} is $N=n$ if~$n>0$ and $N=l+n+1$
% if~$n<0$. If $M>N$, the result is empty. Otherwise it consists of all items from
% position $M$ to position $N$ inclusive; for the purpose of this rule, we can
% imagine that the token list extends at infinity on either side, with void items
% at positions $s$ for $s\le0$ or $s>l$.
% For instance,
% \begin{verbatim}
% \iow_term:x { \str_range:nnn { abcdef } { 2 } { 5 } }
% \iow_term:x { \str_range:nnn { abcdef } { -4 } { -1 } }
% \iow_term:x { \str_range:nnn { abcdef } { -2 } { -1 } }
% \iow_term:x { \str_range:nnn { abcdef } { 0 } { -1 } }
% \end{verbatim}
% prints \texttt{bcde}, \texttt{cdef}, \texttt{ef}, and an empty
% line to the terminal. The \meta{start index} must always be smaller than
% or equal to the \meta{end index}: if this is not the case then no output
% is generated. Thus
% \begin{verbatim}
% \iow_term:x { \str_range:nnn { abcdef } { 5 } { 2 } }
% \iow_term:x { \str_range:nnn { abcdef } { -1 } { -4 } }
% \end{verbatim}
% both yield empty strings.
% \end{function}
%
% ^^A If this stays in the same {function} environment, we get a really
% ^^A awful page break. Perhaps we should add a way to allow a page break
% ^^A in a function environment...
% The behavior of \cs{str_range_ignore_spaces:nnn} is similar, but spaces
% are removed before starting the job. The input
% \begin{verbatim}
% \iow_term:x { \str_range:nnn { abcdefg } { 2 } { 5 } }
% \iow_term:x { \str_range:nnn { abcdefg } { 2 } { -3 } }
% \iow_term:x { \str_range:nnn { abcdefg } { -6 } { 5 } }
% \iow_term:x { \str_range:nnn { abcdefg } { -6 } { -3 } }
%
% \iow_term:x { \str_range:nnn { abc~efg } { 2 } { 5 } }
% \iow_term:x { \str_range:nnn { abc~efg } { 2 } { -3 } }
% \iow_term:x { \str_range:nnn { abc~efg } { -6 } { 5 } }
% \iow_term:x { \str_range:nnn { abc~efg } { -6 } { -3 } }
%
% \iow_term:x { \str_range_ignore_spaces:nnn { abcdefg } { 2 } { 5 } }
% \iow_term:x { \str_range_ignore_spaces:nnn { abcdefg } { 2 } { -3 } }
% \iow_term:x { \str_range_ignore_spaces:nnn { abcdefg } { -6 } { 5 } }
% \iow_term:x { \str_range_ignore_spaces:nnn { abcdefg } { -6 } { -3 } }
%
% \iow_term:x { \str_range_ignore_spaces:nnn { abcd~efg } { 2 } { 5 } }
% \iow_term:x { \str_range_ignore_spaces:nnn { abcd~efg } { 2 } { -3 } }
% \iow_term:x { \str_range_ignore_spaces:nnn { abcd~efg } { -6 } { 5 } }
% \iow_term:x { \str_range_ignore_spaces:nnn { abcd~efg } { -6 } { -3 } }
% \end{verbatim}
% will print four instances of |bcde|, four instances of |bc e| and eight
% instances of |bcde|.
% ^^A\end{function}
%
% \section{Modifying string variables}
%
% \begin{function}[added = 2017-10-08]
% {
% \str_replace_once:Nnn, \str_replace_once:cnn,
% \str_greplace_once:Nnn, \str_greplace_once:cnn
% }
% \begin{syntax}
% \cs{str_replace_once:Nnn} \meta{str~var} \Arg{old} \Arg{new}
% \end{syntax}
% Converts the \meta{old} and \meta{new} token lists to strings, then
% replaces the first (leftmost) occurrence of \meta{old string} in the
% \meta{str~var} with \meta{new string}.
% \end{function}
%
% \begin{function}[added = 2017-10-08]
% {
% \str_replace_all:Nnn, \str_replace_all:cnn,
% \str_greplace_all:Nnn, \str_greplace_all:cnn
% }
% \begin{syntax}
% \cs{str_replace_all:Nnn} \meta{str~var} \Arg{old} \Arg{new}
% \end{syntax}
% Converts the \meta{old} and \meta{new} token lists to strings, then
% replaces all occurrences of \meta{old string} in the
% \meta{str~var} with \meta{new string}.
% As this function
% operates from left to right, the pattern \meta{old string}
% may remain after the replacement (see \cs{str_remove_all:Nn}
% for an example).
% \end{function}
%
% \begin{function}[added = 2017-10-08]
% {
% \str_remove_once:Nn, \str_remove_once:cn,
% \str_gremove_once:Nn, \str_gremove_once:cn
% }
% \begin{syntax}
% \cs{str_remove_once:Nn} \meta{str~var} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} then
% removes the first (leftmost) occurrence of \meta{string} from the
% \meta{str~var}.
% \end{function}
%
% \begin{function}[added = 2017-10-08]
% {
% \str_remove_all:Nn, \str_remove_all:cn,
% \str_gremove_all:Nn, \str_gremove_all:cn
% }
% \begin{syntax}
% \cs{str_remove_all:Nn} \meta{str~var} \Arg{token list}
% \end{syntax}
% Converts the \meta{token list} to a \meta{string} then
% removes all occurrences of \meta{string} from the
% \meta{str~var}.
% As this function
% operates from left to right, the pattern \meta{string}
% may remain after the removal, for instance,
% \begin{quote}
% \cs{str_set:Nn} \cs{l_tmpa_str} |{abbccd}|
% \cs{str_remove_all:Nn} \cs{l_tmpa_str} |{bc}|
% \end{quote}
% results in \cs{l_tmpa_str} containing \texttt{abcd}.
% \end{function}
%
% \section{String manipulation}
%
% \begin{function}[EXP, added = 2019-11-26]
% {
% \str_lowercase:n, \str_lowercase:f,
% \str_uppercase:n, \str_uppercase:f
% }
% \begin{syntax}
% \cs{str_lowercase:n} \Arg{tokens}
% \cs{str_uppercase:n} \Arg{tokens}
% \end{syntax}
% Converts the input \meta{tokens} to their string representation, as
% described for \cs{tl_to_str:n}, and then to the lower or upper
% case representation using a one-to-one mapping as described by the
% Unicode Consortium file |UnicodeData.txt|.
%
% These functions are intended for case changing programmatic data in
% places where upper/lower case distinctions are meaningful. One example
% would be automatically generating a function name from user input where
% some case changing is needed. In this situation the input is programmatic,
% not textual, case does have meaning and a language-independent one-to-one
% mapping is appropriate. For example
% \begin{verbatim}
% \cs_new_protected:Npn \myfunc:nn #1#2
% {
% \cs_set_protected:cpn
% {
% user
% \str_uppercase:f { \tl_head:n {#1} }
% \str_lowercase:f { \tl_tail:n {#1} }
% }
% { #2 }
% }
% \end{verbatim}
% would be used to generate a function with an auto-generated name consisting
% of the upper case equivalent of the supplied name followed by the lower
% case equivalent of the rest of the input.
%
% These functions should \emph{not} be used for
% \begin{itemize}
% \item Caseless comparisons: use \cs{str_foldcase:n} for this
% situation (case folding is distinct from lower casing).
% \item Case changing text for typesetting: see the
% \cs[index=text_lowercase:n]{text_lowercase:n(n)},
% \cs[index=text_uppercase:n]{text_uppercase:n(n)} and
% \cs[index=text_titlecase:n]{text_titlecase:n(n)} functions which
% correctly deal with context-dependence and other factors appropriate
% to text case changing.
% \end{itemize}
% \end{function}
%
% \begin{function}[EXP, added = 2019-11-26]
% {\str_foldcase:n, \str_foldcase:V}
% \begin{syntax}
% \cs{str_foldcase:n} \Arg{tokens}
% \end{syntax}
% Converts the input \meta{tokens} to their string representation, as
% described for \cs{tl_to_str:n}, and then folds the case of the resulting
% \meta{string} to remove case information. The result of this process is
% left in the input stream.
%
% String folding is a process used for material such as identifiers rather
% than for \enquote{text}. The folding provided by \cs{str_foldcase:n}
% follows the mappings provided by the \href{http://www.unicode.org}^^A
% {Unicode Consortium}, who
% \href{http://www.unicode.org/faq/casemap_charprop.html#2}{state}:
% \begin{quote}
% Case folding is primarily used for caseless comparison of text, such
% as identifiers in a computer program, rather than actual text
% transformation. Case folding in Unicode is based on the lowercase
% mapping, but includes additional changes to the source text to help make
% it language-insensitive and consistent. As a result, case-folded text
% should be used solely for internal processing and generally should not be
% stored or displayed to the end user.
% \end{quote}
% The folding approach implemented by \cs{str_foldcase:n} follows the
% \enquote{full} scheme defined by the Unicode Consortium
% (\emph{e.g.}~\SS folds to \texttt{SS}). As case-folding is
% a language-insensitive process, there is no special treatment of
% Turkic input (\emph{i.e.}~\texttt{I} always folds to \texttt{i} and
% not to \texttt{\i}).
% \end{function}
%
% \section{Viewing strings}
%
% \begin{function}[added = 2015-09-18, updated = 2021-04-29]
% {\str_show:N, \str_show:c, \str_show:n}
% \begin{syntax}
% \cs{str_show:N} \meta{str~var}
% \end{syntax}
% Displays the content of the \meta{str~var} on the terminal.
% \end{function}
%
% \begin{function}[added = 2019-02-15, updated = 2021-04-29]
% {\str_log:N, \str_log:c, \str_log:n}
% \begin{syntax}
% \cs{str_log:N} \meta{str~var}
% \end{syntax}
% Writes the content of the \meta{str~var} in the log file.
% \end{function}
%
% \section{Constant strings}
%
% \begin{variable}[added = 2015-09-19, updated = 2020-12-22, module = str]
% {
% \c_ampersand_str,
% \c_atsign_str,
% \c_backslash_str,
% \c_left_brace_str,
% \c_right_brace_str,
% \c_circumflex_str,
% \c_colon_str,
% \c_dollar_str,
% \c_hash_str,
% \c_percent_str,
% \c_tilde_str,
% \c_underscore_str,
% \c_zero_str
% }
% Constant strings, containing a single character token, with category
% code $12$.
% \end{variable}
%
% \section{Scratch strings}
%
% \begin{variable}{\l_tmpa_str, \l_tmpb_str}
% Scratch strings for local assignment. These are never used by
% the kernel code, and so are safe for use with any \LaTeX3-defined
% function. However, they may be overwritten by other non-kernel
% code and so should only be used for short-term storage.
% \end{variable}
%
% \begin{variable}{\g_tmpa_str, \g_tmpb_str}
% Scratch strings for global assignment. These are never used by
% the kernel code, and so are safe for use with any \LaTeX3-defined
% function. However, they may be overwritten by other non-kernel
% code and so should only be used for short-term storage.
% \end{variable}
%
% \end{documentation}
%
% \begin{implementation}
%
% \section{\pkg{l3str} implementation}
%
% \begin{macrocode}
%<*package>
% \end{macrocode}
%
% \begin{macrocode}
%<@@=str>
% \end{macrocode}
%
% \subsection{Internal auxiliaries}
%
% \begin{variable}{\s_@@_mark,\s_@@_stop}
% Internal scan marks.
% \begin{macrocode}
\scan_new:N \s_@@_mark
\scan_new:N \s_@@_stop
% \end{macrocode}
% \end{variable}
%
% \begin{macro}[EXP]{
% \@@_use_none_delimit_by_s_stop:w,
% \@@_use_i_delimit_by_s_stop:nw
% }
% Functions to gobble up to a scan mark.
% \begin{macrocode}
\cs_new:Npn \@@_use_none_delimit_by_s_stop:w #1 \s_@@_stop { }
\cs_new:Npn \@@_use_i_delimit_by_s_stop:nw #1 #2 \s_@@_stop {#1}
% \end{macrocode}
% \end{macro}
%
% \begin{variable}{\q_@@_recursion_tail,\q_@@_recursion_stop}
% Internal recursion quarks.
% \begin{macrocode}
\quark_new:N \q_@@_recursion_tail
\quark_new:N \q_@@_recursion_stop
% \end{macrocode}
% \end{variable}
%
% \begin{macro}[EXP]{
% \@@_if_recursion_tail_break:NN,
% \@@_if_recursion_tail_stop_do:Nn
% }
% Functions to query recursion quarks.
% \begin{macrocode}
\__kernel_quark_new_test:N \@@_if_recursion_tail_break:NN
\__kernel_quark_new_test:N \@@_if_recursion_tail_stop_do:Nn
% \end{macrocode}
% \end{macro}
%
% \subsection{Creating and setting string variables}
%
% \begin{macro}
% {
% \str_new:N, \str_new:c,
% \str_use:N, \str_use:c,
% \str_clear:N, \str_clear:c,
% \str_gclear:N,\str_gclear:c,
% \str_clear_new:N, \str_clear_new:c,
% \str_gclear_new:N, \str_gclear_new:c
% }
% \begin{macro}
% {
% \str_set_eq:NN, \str_set_eq:cN, \str_set_eq:Nc, \str_set_eq:cc,
% \str_gset_eq:NN, \str_gset_eq:cN, \str_gset_eq:Nc, \str_gset_eq:cc
% }
% \begin{macro}
% {\str_concat:NNN, \str_concat:ccc, \str_gconcat:NNN, \str_gconcat:ccc}
% A string is simply a token list. The full mapping system isn't set up
% yet so do things by hand.
% \begin{macrocode}
\group_begin:
\cs_set_protected:Npn \@@_tmp:n #1
{
\tl_if_blank:nF {#1}
{
\cs_new_eq:cc { str_ #1 :N } { tl_ #1 :N }
\exp_args:Nc \cs_generate_variant:Nn { str_ #1 :N } { c }
\@@_tmp:n
}
}
\@@_tmp:n
{ new }
{ use }
{ clear }
{ gclear }
{ clear_new }
{ gclear_new }
{ }
\group_end:
\cs_new_eq:NN \str_set_eq:NN \tl_set_eq:NN
\cs_new_eq:NN \str_gset_eq:NN \tl_gset_eq:NN
\cs_generate_variant:Nn \str_set_eq:NN { c , Nc , cc }
\cs_generate_variant:Nn \str_gset_eq:NN { c , Nc , cc }
\cs_new_eq:NN \str_concat:NNN \tl_concat:NNN
\cs_new_eq:NN \str_gconcat:NNN \tl_gconcat:NNN
\cs_generate_variant:Nn \str_concat:NNN { ccc }
\cs_generate_variant:Nn \str_gconcat:NNN { ccc }
% \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}
% {
% \str_set:Nn, \str_set:NV, \str_set:Nx,
% \str_set:cn, \str_set:cV, \str_set:cx,
% \str_gset:Nn, \str_gset:NV, \str_gset:Nx,
% \str_gset:cn, \str_gset:cV, \str_gset:cx,
% \str_const:Nn, \str_const:NV, \str_const:Nx,
% \str_const:cn, \str_const:cV, \str_const:cx,
% \str_put_left:Nn, \str_put_left:NV, \str_put_left:Nx,
% \str_put_left:cn, \str_put_left:cV, \str_put_left:cx,
% \str_gput_left:Nn, \str_gput_left:NV, \str_gput_left:Nx,
% \str_gput_left:cn, \str_gput_left:cV, \str_gput_left:cx,
% \str_put_right:Nn, \str_put_right:NV, \str_put_right:Nx,
% \str_put_right:cn, \str_put_right:cV, \str_put_right:cx,
% \str_gput_right:Nn, \str_gput_right:NV, \str_gput_right:Nx,
% \str_gput_right:cn, \str_gput_right:cV, \str_gput_right:cx
% }
% Simply convert the token list inputs to \meta{strings}.
% \begin{macrocode}
\group_begin:
\cs_set_protected:Npn \@@_tmp:n #1
{
\tl_if_blank:nF {#1}
{
\cs_new_protected:cpx { str_ #1 :Nn } ##1##2
{
\exp_not:c { tl_ #1 :Nx } ##1
{ \exp_not:N \tl_to_str:n {##2} }
}
\cs_generate_variant:cn { str_ #1 :Nn } { NV , Nx , cn , cV , cx }
\@@_tmp:n
}
}
\@@_tmp:n
{ set }
{ gset }
{ const }
{ put_left }
{ gput_left }
{ put_right }
{ gput_right }
{ }
\group_end:
% \end{macrocode}
% \end{macro}
%
% \subsection{Modifying string variables}
%