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l3prg.dtx
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l3prg.dtx
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% \iffalse meta-comment
%
%% File: l3prg.dtx Copyright (C) 2005-2018 The LaTeX3 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{l3prg} package\\ Control structures^^A
% }
%
% \author{^^A
% The \LaTeX3 Project\thanks
% {^^A
% E-mail:
% \href{mailto:latex-team@latex-project.org}
% {latex-team@latex-project.org}^^A
% }^^A
% }
%
% \date{Released 2018/03/05}
%
% \maketitle
%
% \begin{documentation}
%
% Conditional processing in \LaTeX3 is defined as something that
% performs a series of tests, possibly involving assignments and
% calling other functions that do not read further ahead in the input
% stream. After processing the input, a \emph{state} is returned. The
% states returned are \meta{true} and \meta{false}.
%
% \LaTeX3 has two forms of conditional flow processing based
% on these states. The first form is predicate functions that turn the
% returned state into a boolean \meta{true} or \meta{false}. For
% example, the function \cs{cs_if_free_p:N} checks whether the control
% sequence given as its argument is free and then returns the boolean
% \meta{true} or \meta{false} values to be used in testing with
% \cs{if_predicate:w} or in functions to be described below. The second form
% is the kind of functions choosing a particular argument from the
% input stream based on the result of the testing as in
% \cs{cs_if_free:NTF} which also takes one argument (the |N|) and then
% executes either \texttt{true} or \texttt{false} depending on the
% result.
%
% \begin{texnote}
% The arguments are executed after exiting the underlying
% |\if...\fi:| structure.
% \end{texnote}
%
% \section{Defining a set of conditional functions}
% \label{sec:l3prg:new-conditional-functions}
%
% \begin{function}[updated = 2012-02-06]
% {
% \prg_new_conditional:Npnn, \prg_set_conditional:Npnn,
% \prg_new_conditional:Nnn, \prg_set_conditional:Nnn
% }
% \begin{syntax}
% \cs{prg_new_conditional:Npnn} \cs[no-index]{\meta{name}:\meta{arg spec}} \meta{parameters} \Arg{conditions} \Arg{code} \\
% \cs{prg_new_conditional:Nnn} \cs[no-index]{\meta{name}:\meta{arg spec}} \Arg{conditions} \Arg{code}
% \end{syntax}
% These functions create a family of conditionals using the same
% \Arg{code} to perform the test created. Those conditionals are
% expandable if \meta{code} is. The \texttt{new} versions check
% for existing definitions and perform assignments globally
% (\emph{cf.}~\cs{cs_new:Npn}) whereas the \texttt{set} versions do no
% check and perform assignments locally (\emph{cf.}~\cs{cs_set:Npn}).
% The conditionals created are dependent on the comma-separated list
% of \meta{conditions}, which should be one or more of \texttt{p},
% \texttt{T}, \texttt{F} and \texttt{TF}.
% \end{function}
%
% \begin{function}[updated = 2012-02-06]
% {
% \prg_new_protected_conditional:Npnn, \prg_set_protected_conditional:Npnn,
% \prg_new_protected_conditional:Nnn, \prg_set_protected_conditional:Nnn
% }
% \begin{syntax}
% \cs{prg_new_protected_conditional:Npnn} \cs[no-index]{\meta{name}:\meta{arg spec}} \meta{parameters} \Arg{conditions} \Arg{code} \\
% \cs{prg_new_protected_conditional:Nnn} \cs[no-index]{\meta{name}:\meta{arg spec}} \Arg{conditions} \Arg{code}
% \end{syntax}
% These functions create a family of protected conditionals using the
% same \Arg{code} to perform the test created. The \meta{code} does
% not need to be expandable. The \texttt{new} version check for
% existing definitions and perform assignments globally
% (\emph{cf.}~\cs{cs_new:Npn}) whereas the \texttt{set} version do
% not (\emph{cf.}~\cs{cs_set:Npn}). The conditionals created are
% depended on the comma-separated list of \meta{conditions}, which
% should be one or more of \texttt{T}, \texttt{F} and \texttt{TF} (not
% \texttt{p}).
% \end{function}
%
% The conditionals are defined by \cs{prg_new_conditional:Npnn} and
% friends as:
% \begin{itemize}
% \item \cs[no-index]{\meta{name}_p:\meta{arg spec}} --- a predicate function
% which will supply either a logical \texttt{true} or logical
% \texttt{false}. This function is intended for use in cases where
% one or more logical tests are combined to lead to a final outcome.
% This function cannot be defined for \texttt{protected}
% conditionals.
% \item \cs[no-index]{\meta{name}:\meta{arg spec}T} --- a function with one more
% argument than the original \meta{arg spec} demands. The \meta{true
% branch} code in this additional argument will be left on the
% input stream only if the test is \texttt{true}.
% \item \cs[no-index]{\meta{name}:\meta{arg spec}F} --- a function with one more
% argument than the original \meta{arg spec} demands. The
% \meta{false branch} code in this additional argument will be left
% on the input stream only if the test is \texttt{false}.
% \item \cs[no-index]{\meta{name}:\meta{arg spec}TF} --- a function with two
% more argument than the original \meta{arg spec} demands. The
% \meta{true branch} code in the first additional argument will be
% left on the input stream if the test is \texttt{true}, while the
% \meta{false branch} code in the second argument will be left on
% the input stream if the test is \texttt{false}.
% \end{itemize}
% The \meta{code} of the test may use \meta{parameters} as specified by
% the second argument to \cs{prg_set_conditional:Npnn}: this should
% match the \meta{argument specification} but this is not enforced. The
% |Nnn| versions infer the number of arguments from the argument
% specification given (\emph{cf.}~\cs{cs_new:Nn}, \emph{etc.}). Within
% the \meta{code}, the functions \cs{prg_return_true:} and
% \cs{prg_return_false:} are used to indicate the logical outcomes of
% the test.
%
% An example can easily clarify matters here:
% \begin{verbatim}
% \prg_set_conditional:Npnn \foo_if_bar:NN #1#2 { p , T , TF }
% {
% \if_meaning:w \l_tmpa_tl #1
% \prg_return_true:
% \else:
% \if_meaning:w \l_tmpa_tl #2
% \prg_return_true:
% \else:
% \prg_return_false:
% \fi:
% \fi:
% }
% \end{verbatim}
% This defines the function |\foo_if_bar_p:NN|, |\foo_if_bar:NNTF| and
% |\foo_if_bar:NNT| but not |\foo_if_bar:NNF| (because |F| is missing
% from the \meta{conditions} list). The return statements take care of
% resolving the remaining \cs{else:} and \cs{fi:} before returning the
% state. There must be a return statement for each branch; failing to do
% so will result in erroneous output if that branch is executed.
%
% \begin{function}{\prg_new_eq_conditional:NNn, \prg_set_eq_conditional:NNn}
% \begin{syntax}
% \cs{prg_new_eq_conditional:NNn} \cs[no-index]{\meta{name_1}:\meta{arg spec_1}} \cs[no-index]{\meta{name_2}:\meta{arg spec_2}} \Arg{conditions}
% \end{syntax}
% These functions copy a family of conditionals. The \texttt{new} version
% checks for existing definitions (\emph{cf.}~\cs{cs_new_eq:NN}) whereas
% the \texttt{set} version does not (\emph{cf.}~\cs{cs_set_eq:NN}). The
% conditionals copied are depended on the comma-separated list of
% \meta{conditions}, which should be one or more of \texttt{p}, \texttt{T},
% \texttt{F} and \texttt{TF}.
% \end{function}
%
% \begin{function}[EXP]{\prg_return_true:, \prg_return_false:}
% \begin{syntax}
% \cs{prg_return_true:}
% \cs{prg_return_false:}
% \end{syntax}
% These \enquote{return} functions define the logical state of a conditional statement.
% They appear within the code for a conditional
% function generated by \cs{prg_set_conditional:Npnn}, \emph{etc}, to indicate
% when a true or false branch should be taken.
% While they may appear multiple times each within the code of such conditionals,
% the execution of the conditional must result in the expansion of one of these
% two functions \emph{exactly once}.
%
% The return functions trigger what is internally an \texttt{f}-expansion process to complete
% the evaluation of the conditional. Therefore, after \cs{prg_return_true:} or \cs{prg_return_false:}
% there must be no non-expandable material in the input stream for the remainder of
% the expansion of the conditional code. This includes other instances of either of these functions.
% \end{function}
%
% \section{The boolean data type}
%
% This section describes a boolean data type which is closely
% connected to conditional processing as sometimes you want to
% execute some code depending on the value of a switch
% (\emph{e.g.},~draft/final) and other times you perhaps want to use it as a
% predicate function in an \cs{if_predicate:w} test. The problem of the
% primitive \cs{if_false:} and \cs{if_true:} tokens is that it is not
% always safe to pass them around as they may interfere with scanning
% for termination of primitive conditional processing. Therefore, we
% employ two canonical booleans: \cs{c_true_bool} or
% \cs{c_false_bool}. Besides preventing problems as described above, it
% also allows us to implement a simple boolean parser supporting the
% logical operations And, Or, Not, \emph{etc.}\ which can then be used on
% both the boolean type and predicate functions.
%
% All conditional |\bool_| functions except assignments are expandable
% and expect the input to also be fully expandable (which generally
% means being constructed from predicate functions and booleans, possibly nested).
%
% \begin{texnote}
% The \texttt{bool} data type is not implemented using the
% \tn{iffalse}/\tn{iftrue} primitives, in contrast to \tn{newif},
% \emph{etc.}, in plain \TeX{}, \LaTeXe{} and so on. Programmers should
% not base use of \texttt{bool} switches on any particular expectation
% of the implementation.
% \end{texnote}
%
% \begin{function}{\bool_new:N, \bool_new:c}
% \begin{syntax}
% \cs{bool_new:N} \meta{boolean}
% \end{syntax}
% Creates a new \meta{boolean} or raises an error if the
% name is already taken. The declaration is global. The
% \meta{boolean} is initially \texttt{false}.
% \end{function}
%
% \begin{function}
% {
% \bool_set_false:N , \bool_set_false:c ,
% \bool_gset_false:N, \bool_gset_false:c
% }
% \begin{syntax}
% \cs{bool_set_false:N} \meta{boolean}
% \end{syntax}
% Sets \meta{boolean} logically \texttt{false}.
% \end{function}
%
% \begin{function}
% {
% \bool_set_true:N , \bool_set_true:c ,
% \bool_gset_true:N , \bool_gset_true:c
% }
% \begin{syntax}
% \cs{bool_set_true:N} \meta{boolean}
% \end{syntax}
% Sets \meta{boolean} logically \texttt{true}.
% \end{function}
%
% \begin{function}
% {
% \bool_set_eq:NN , \bool_set_eq:cN , \bool_set_eq:Nc , \bool_set_eq:cc ,
% \bool_gset_eq:NN, \bool_gset_eq:cN, \bool_gset_eq:Nc, \bool_gset_eq:cc
% }
% \begin{syntax}
% \cs{bool_set_eq:NN} \meta{boolean_1} \meta{boolean_2}
% \end{syntax}
% Sets \meta{boolean_1} to the current value of \meta{boolean_2}.
% \end{function}
%
% \begin{function}[updated = 2017-07-15]
% {\bool_set:Nn, \bool_set:cn, \bool_gset:Nn, \bool_gset:cn}
% \begin{syntax}
% \cs{bool_set:Nn} \meta{boolean} \Arg{boolexpr}
% \end{syntax}
% Evaluates the \meta{boolean expression} as described for
% \cs{bool_if:nTF}, and sets the \meta{boolean} variable to
% the logical truth of this evaluation.
% \end{function}
%
% \begin{function}[EXP,pTF, updated = 2017-07-15]{\bool_if:N, \bool_if:c}
% \begin{syntax}
% \cs{bool_if_p:N} \meta{boolean}
% \cs{bool_if:NTF} \meta{boolean} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests the current truth of \meta{boolean}, and continues expansion
% based on this result.
% \end{function}
%
% \begin{function}[added = 2012-02-09, updated = 2015-08-01]{\bool_show:N, \bool_show:c}
% \begin{syntax}
% \cs{bool_show:N} \meta{boolean}
% \end{syntax}
% Displays the logical truth of the \meta{boolean} on the terminal.
% \end{function}
%
% \begin{function}[added = 2012-02-09, updated = 2017-07-15]{\bool_show:n}
% \begin{syntax}
% \cs{bool_show:n} \Arg{boolean expression}
% \end{syntax}
% Displays the logical truth of the \meta{boolean expression} on the
% terminal.
% \end{function}
%
% \begin{function}[added = 2014-08-22, updated = 2015-08-03]{\bool_log:N, \bool_log:c}
% \begin{syntax}
% \cs{bool_log:N} \meta{boolean}
% \end{syntax}
% Writes the logical truth of the \meta{boolean} in the log file.
% \end{function}
%
% \begin{function}[added = 2014-08-22, updated = 2017-07-15]{\bool_log:n}
% \begin{syntax}
% \cs{bool_log:n} \Arg{boolean expression}
% \end{syntax}
% Writes the logical truth of the \meta{boolean expression} in the log
% file.
% \end{function}
%
% \begin{function}[EXP, pTF, added=2012-03-03]
% {\bool_if_exist:N, \bool_if_exist:c}
% \begin{syntax}
% \cs{bool_if_exist_p:N} \meta{boolean}
% \cs{bool_if_exist:NTF} \meta{boolean} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests whether the \meta{boolean} is currently defined. This does not
% check that the \meta{boolean} really is a boolean variable.
% \end{function}
%
% \begin{variable}{\l_tmpa_bool, \l_tmpb_bool}
% A scratch boolean for local assignment. It is never used by
% the kernel code, and so is safe for use with any \LaTeX3-defined
% function. However, it may be overwritten by other non-kernel
% code and so should only be used for short-term storage.
% \end{variable}
%
% \begin{variable}{\g_tmpa_bool, \g_tmpb_bool}
% A scratch boolean for global assignment. It is never used by
% the kernel code, and so is safe for use with any \LaTeX3-defined
% function. However, it may be overwritten by other non-kernel
% code and so should only be used for short-term storage.
% \end{variable}
%
% \section{Boolean expressions}
%
% As we have a boolean datatype and predicate functions returning
% boolean \meta{true} or \meta{false} values, it seems only fitting
% that we also provide a parser for \meta{boolean expressions}.
%
% A boolean expression is an expression which given input in the form
% of predicate functions and boolean variables, return boolean
% \meta{true} or \meta{false}. It supports the logical operations And,
% Or and Not as the well-known infix operators |&&| and \verb"||" and prefix~|!|
% with their usual precedences (namely, |&&| binds more tightly than
% \verb"||"). In addition to this, parentheses can be used to isolate
% sub-expressions. For example,
% \begin{verbatim}
% \int_compare_p:n { 1 = 1 } &&
% (
% \int_compare_p:n { 2 = 3 } ||
% \int_compare_p:n { 4 <= 4 } ||
% \str_if_eq_p:nn { abc } { def }
% ) &&
% ! \int_compare_p:n { 2 = 4 }
% \end{verbatim}
% is a valid boolean expression.
%
% Contrarily to some other programming languages, the operators |&&| and
% \verb"||" evaluate both operands in all cases, even when the first
% operand is enough to determine the result. This \enquote{eager}
% evaluation should be contrasted with the \enquote{lazy} evaluation of
% \cs[no-index]{bool_lazy_\ldots{}} functions.
%
% \begin{texnote}
% The eager evaluation of boolean expressions is unfortunately
% necessary in \TeX{}. Indeed, a lazy parser can get confused if |&&|
% or \verb"||" or parentheses appear as (unbraced) arguments of some
% predicates. For instance, the innocuous-looking expression below
% would break (in a lazy parser) if |#1| were a closing parenthesis
% and \cs[no-index]{l_tmpa_bool} were \texttt{true}.
% \begin{verbatim}
% ( \l_tmpa_bool || \token_if_eq_meaning_p:NN X #1 )
% \end{verbatim}
% \end{texnote}
%
% Minimal (lazy) evaluation can be obtained using the conditionals
% \cs{bool_lazy_all:nTF}, \cs{bool_lazy_and:nnTF}, \cs{bool_lazy_any:nTF}, or
% \cs{bool_lazy_or:nnTF}, which only evaluate their boolean expression
% arguments when they are needed to determine the resulting truth
% value. For example, when evaluating the boolean expression
% \begin{verbatim}
% \bool_lazy_and_p:nn
% {
% \bool_lazy_any_p:n
% {
% { \int_compare_p:n { 2 = 3 } }
% { \int_compare_p:n { 4 <= 4 } }
% { \int_compare_p:n { 1 = \error } } % skipped
% }
% }
% { ! \int_compare_p:n { 2 = 4 } }
% \end{verbatim}
% the line marked with |skipped| is not expanded because the result
% of \cs{bool_lazy_any_p:n} is known once the second boolean expression is
% found to be logically \texttt{true}. On the other hand, the last
% line is expanded because its logical value is needed to determine the
% result of \cs{bool_lazy_and_p:nn}.
%
% \begin{function}[EXP, pTF, updated = 2017-07-15]{\bool_if:n}
% \begin{syntax}
% \cs{bool_if_p:n} \Arg{boolean expression}
% \cs{bool_if:nTF} \Arg{boolean expression} \Arg{true code} \Arg{false code}
% \end{syntax}
% Tests the current truth of \meta{boolean expression}, and
% continues expansion based on this result. The
% \meta{boolean expression} should consist of a series of predicates
% or boolean variables with the logical relationship between these
% defined using |&&| (\enquote{And}), \verb"||" (\enquote{Or}),
% |!| (\enquote{Not}) and parentheses. The logical Not applies to
% the next predicate or group.
% \end{function}
%
% \begin{function}[EXP, pTF, added = 2015-11-15, updated = 2017-07-15]{\bool_lazy_all:n}
% \begin{syntax}
% \cs{bool_lazy_all_p:n} \{ \Arg{boolexpr_1} \Arg{boolexpr_2} $\cdots$ \Arg{boolexpr_N} \}
% \cs{bool_lazy_all:nTF} \{ \Arg{boolexpr_1} \Arg{boolexpr_2} $\cdots$ \Arg{boolexpr_N} \} \Arg{true code} \Arg{false code}
% \end{syntax}
% Implements the \enquote{And} operation on the \meta{boolean
% expressions}, hence is \texttt{true} if all of them are
% \texttt{true} and \texttt{false} if any of them is \texttt{false}.
% Contrarily to the infix operator |&&|, only the \meta{boolean
% expressions} which are needed to determine the result of
% \cs{bool_lazy_all:nTF} are evaluated. See also \cs{bool_lazy_and:nnTF}
% when there are only two \meta{boolean expressions}.
% \end{function}
%
% \begin{function}[EXP, pTF, added = 2015-11-15, updated = 2017-07-15]{\bool_lazy_and:nn}
% \begin{syntax}
% \cs{bool_lazy_and_p:nn} \Arg{boolexpr_1} \Arg{boolexpr_2}
% \cs{bool_lazy_and:nnTF} \Arg{boolexpr_1} \Arg{boolexpr_2} \Arg{true code} \Arg{false code}
% \end{syntax}
% Implements the \enquote{And} operation between two boolean
% expressions, hence is \texttt{true} if both are \texttt{true}.
% Contrarily to the infix operator |&&|, the \meta{boolexpr_2} is only
% evaluated if it is needed to determine the result of
% \cs{bool_lazy_and:nnTF}. See also \cs{bool_lazy_all:nTF} when there are more
% than two \meta{boolean expressions}.
% \end{function}
%
% \begin{function}[EXP, pTF, added = 2015-11-15, updated = 2017-07-15]{\bool_lazy_any:n}
% \begin{syntax}
% \cs{bool_lazy_any_p:n} \{ \Arg{boolexpr_1} \Arg{boolexpr_2} $\cdots$ \Arg{boolexpr_N} \}
% \cs{bool_lazy_any:nTF} \{ \Arg{boolexpr_1} \Arg{boolexpr_2} $\cdots$ \Arg{boolexpr_N} \} \Arg{true code} \Arg{false code}
% \end{syntax}
% Implements the \enquote{Or} operation on the \meta{boolean
% expressions}, hence is \texttt{true} if any of them is
% \texttt{true} and \texttt{false} if all of them are \texttt{false}.
% Contrarily to the infix operator \verb"||", only the \meta{boolean
% expressions} which are needed to determine the result of
% \cs{bool_lazy_any:nTF} are evaluated. See also \cs{bool_lazy_or:nnTF}
% when there are only two \meta{boolean expressions}.
% \end{function}
%
% \begin{function}[EXP, pTF, added = 2015-11-15, updated = 2017-07-15]{\bool_lazy_or:nn}
% \begin{syntax}
% \cs{bool_lazy_or_p:nn} \Arg{boolexpr_1} \Arg{boolexpr_2}
% \cs{bool_lazy_or:nnTF} \Arg{boolexpr_1} \Arg{boolexpr_2} \Arg{true code} \Arg{false code}
% \end{syntax}
% Implements the \enquote{Or} operation between two boolean
% expressions, hence is \texttt{true} if either one is \texttt{true}.
% Contrarily to the infix operator \verb"||", the \meta{boolexpr_2}
% is only evaluated if it is needed to determine the result of
% \cs{bool_lazy_or:nnTF}. See also \cs{bool_lazy_any:nTF} when there are more
% than two \meta{boolean expressions}.
% \end{function}
%
% \begin{function}[EXP, updated = 2017-07-15]{\bool_not_p:n}
% \begin{syntax}
% \cs{bool_not_p:n} \Arg{boolean expression}
% \end{syntax}
% Function version of |!(|\meta{boolean expression}|)| within a boolean
% expression.
% \end{function}
%
% \begin{function}[EXP, updated = 2017-07-15]{\bool_xor_p:nn}
% \begin{syntax}
% \cs{bool_xor_p:nn} \Arg{boolexpr_1} \Arg{boolexpr_2}
% \end{syntax}
% Implements an \enquote{exclusive or} operation between two boolean
% expressions. There is no infix operation for this logical
% operator.
% \end{function}
%
% \section{Logical loops}
%
% Loops using either boolean expressions or stored boolean values.
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_do_until:Nn, \bool_do_until:cn}
% \begin{syntax}
% \cs{bool_do_until:Nn} \meta{boolean} \Arg{code}
% \end{syntax}
% Places the \meta{code} in the input stream for \TeX{} to process,
% and then checks the logical value of the \meta{boolean}. If it is
% \texttt{false} then the \meta{code} is inserted into the input
% stream again and the process loops until the \meta{boolean} is
% \texttt{true}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_do_while:Nn, \bool_do_while:cn}
% \begin{syntax}
% \cs{bool_do_while:Nn} \meta{boolean} \Arg{code}
% \end{syntax}
% Places the \meta{code} in the input stream for \TeX{} to process,
% and then checks the logical value of the \meta{boolean}. If it is
% \texttt{true} then the \meta{code} is inserted into the input
% stream again and the process loops until the \meta{boolean} is
% \texttt{false}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_until_do:Nn, \bool_until_do:cn}
% \begin{syntax}
% \cs{bool_until_do:Nn} \meta{boolean} \Arg{code}
% \end{syntax}
% This function firsts checks the logical value of the \meta{boolean}.
% If it is \texttt{false} the \meta{code} is placed in the input stream
% and expanded. After the completion of the \meta{code} the truth
% of the \meta{boolean} is re-evaluated. The process then loops
% until the \meta{boolean} is \texttt{true}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_while_do:Nn, \bool_while_do:cn}
% \begin{syntax}
% \cs{bool_while_do:Nn} \meta{boolean} \Arg{code}
% \end{syntax}
% This function firsts checks the logical value of the \meta{boolean}.
% If it is \texttt{true} the \meta{code} is placed in the input stream
% and expanded. After the completion of the \meta{code} the truth
% of the \meta{boolean} is re-evaluated. The process then loops
% until the \meta{boolean} is \texttt{false}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_do_until:nn}
% \begin{syntax}
% \cs{bool_do_until:nn} \Arg{boolean expression} \Arg{code}
% \end{syntax}
% Places the \meta{code} in the input stream for \TeX{} to process,
% and then checks the logical value of the \meta{boolean expression}
% as described for \cs{bool_if:nTF}. If it is \texttt{false} then the
% \meta{code} is inserted into the input stream again and the
% process loops until the \meta{boolean expression} evaluates to
% \texttt{true}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_do_while:nn}
% \begin{syntax}
% \cs{bool_do_while:nn} \Arg{boolean expression} \Arg{code}
% \end{syntax}
% Places the \meta{code} in the input stream for \TeX{} to process,
% and then checks the logical value of the \meta{boolean expression}
% as described for \cs{bool_if:nTF}. If it is \texttt{true} then the
% \meta{code} is inserted into the input stream again and the
% process loops until the \meta{boolean expression} evaluates to
% \texttt{false}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_until_do:nn}
% \begin{syntax}
% \cs{bool_until_do:nn} \Arg{boolean expression} \Arg{code}
% \end{syntax}
% This function firsts checks the logical value of the
% \meta{boolean expression} (as described for \cs{bool_if:nTF}).
% If it is \texttt{false} the \meta{code} is placed in the input stream
% and expanded. After the completion of the \meta{code} the truth
% of the \meta{boolean expression} is re-evaluated. The process
% then loops until the \meta{boolean expression} is \texttt{true}.
% \end{function}
%
% \begin{function}[rEXP, updated = 2017-07-15]{\bool_while_do:nn}
% \begin{syntax}
% \cs{bool_while_do:nn} \Arg{boolean expression} \Arg{code}
% \end{syntax}
% This function firsts checks the logical value of the
% \meta{boolean expression} (as described for \cs{bool_if:nTF}).
% If it is \texttt{true} the \meta{code} is placed in the input stream
% and expanded. After the completion of the \meta{code} the truth
% of the \meta{boolean expression} is re-evaluated. The process
% then loops until the \meta{boolean expression} is \texttt{false}.
% \end{function}
%
% \section{Producing multiple copies}
%
% \begin{function}[updated = 2011-07-04, EXP]{\prg_replicate:nn}
% \begin{syntax}
% \cs{prg_replicate:nn} \Arg{integer expression} \Arg{tokens}
% \end{syntax}
% Evaluates the \meta{integer expression} (which should be
% zero or positive) and creates the resulting number of copies
% of the \meta{tokens}. The function is both expandable and safe for
% nesting. It yields its result after two expansion steps.
% \end{function}
%
% \section{Detecting \TeX{}'s mode}
%
% \begin{function}[EXP,pTF]{\mode_if_horizontal:}
% \begin{syntax}
% \cs{mode_if_horizontal_p:}
% \cs{mode_if_horizontal:TF} \Arg{true code} \Arg{false code}
% \end{syntax}
% Detects if \TeX{} is currently in horizontal mode.
% \end{function}
%
% \begin{function}[EXP,pTF]{\mode_if_inner:}
% \begin{syntax}
% \cs{mode_if_inner_p:}
% \cs{mode_if_inner:TF} \Arg{true code} \Arg{false code}
% \end{syntax}
% Detects if \TeX{} is currently in inner mode.
% \end{function}
%
% \begin{function}[updated = 2011-09-05, EXP,pTF]{\mode_if_math:}
% \begin{syntax}
% \cs{mode_if_math:TF} \Arg{true code} \Arg{false code}
% \end{syntax}
% Detects if \TeX{} is currently in maths mode.
% \end{function}
%
% \begin{function}[EXP,pTF]{\mode_if_vertical:}
% \begin{syntax}
% \cs{mode_if_vertical_p:}
% \cs{mode_if_vertical:TF} \Arg{true code} \Arg{false code}
% \end{syntax}
% Detects if \TeX{} is currently in vertical mode.
% \end{function}
%
% \section{Primitive conditionals}
%
% \begin{function}[EXP]{\if_predicate:w}
% \begin{syntax}
% \cs{if_predicate:w} \meta{predicate} \meta{true code} \cs{else:} \meta{false code} \cs{fi:}
% \end{syntax}
% This function takes a predicate function and
% branches according to the result. (In practice this function would also
% accept a single boolean variable in place of the \meta{predicate} but to make the
% coding clearer this should be done through \cs{if_bool:N}.)
% \end{function}
%
% \begin{function}[EXP]{\if_bool:N}
% \begin{syntax}
% \cs{if_bool:N} \meta{boolean} \meta{true code} \cs{else:} \meta{false code} \cs{fi:}
% \end{syntax}
% This function takes a boolean variable and
% branches according to the result.
% \end{function}
%
% \section{Nestable recursions and mappings}
%
% There are a number of places where recursion or mapping constructs are used in
% \pkg{expl3}. At a low-level, these typically require insertion of tokens
% at the end of the content to allow \enquote{clean up}. To support such
% mappings in a nestable form, the following functions are provided.
%
% \begin{function}[EXP, added = 2018-03-26]{\prg_break_point:Nn}
% \begin{syntax}
% \cs{prg_break_point:Nn} \cs[no-index]{\meta{type}_map_break:} \Arg{code}
% \end{syntax}
% Used to mark the end of a recursion or mapping: the functions
% \cs[no-index]{\meta{type}_map_break:} and
% \cs[no-index]{\meta{type}_map_break:n} use this to break out of the loop
% (see \cs{prg_map_break:Nn} for how to set these up).
% After the loop ends, the \meta{code} is inserted into the input stream. This
% occurs even if the break functions are \emph{not} applied:
% \cs{prg_break_point:Nn} is functionally-equivalent in these cases
% to \cs{use_ii:nn}.
% \end{function}
%
% \begin{function}[EXP, added = 2018-03-26]{\prg_map_break:Nn}
% \begin{syntax}
% \cs{prg_map_break:Nn} \cs[no-index]{\meta{type}_map_break:} \Arg{user code}
% \ldots{}
% \cs{prg_break_point:Nn} \cs[no-index]{\meta{type}_map_break:} \Arg{ending code}
% \end{syntax}
% Breaks a recursion in mapping contexts, inserting in the input
% stream the \meta{user code} after the \meta{ending code} for the
% loop. The function breaks loops, inserting their \meta{ending
% code}, until reaching a loop with the same \meta{type} as its
% first argument. This \cs[no-index]{\meta{type}_map_break:} argument is
% simply used as a recognizable marker for the \meta{type}.
% \end{function}
%
% \section{Internal programming functions}
%
% \begin{function}[updated = 2011-08-11, EXP]
% {\group_align_safe_begin:, \group_align_safe_end:}
% \begin{syntax}
% \cs{group_align_safe_begin:}
% \ldots
% \cs{group_align_safe_end:}
% \end{syntax}
% These functions are used to enclose material in a \TeX{} alignment
% environment within a specially-constructed group. This group is
% designed in such a way that it does not add brace groups to the
% output but does act as a group for the |&| token inside
% \tn{halign}. This is necessary to allow grabbing of tokens
% for testing purposes, as \TeX{} uses group level to determine the
% effect of alignment tokens. Without the special grouping, the use of
% a function such as \cs{peek_after:Nw} would result in a forbidden
% comparison of the internal \tn{endtemplate} token, yielding a
% fatal error. Each \cs{group_align_safe_begin:} must be matched by a
% \cs{group_align_safe_end:}, although this does not have to occur
% within the same function.
% \end{function}
%
% \begin{variable}{\g__prg_map_int}
% This integer is used by non-expandable mapping functions to track
% the level of nesting in force. The functions \cs{__prg_map_1:w},
% \cs{__prg_map_2:w}, \emph{etc.}, labelled by \cs{g__prg_map_int}
% hold functions to be mapped over various list datatypes in inline
% and variable mappings.
% \end{variable}
%
% \begin{function}[EXP]{\__prg_break_point:}
% This copy of \cs{prg_do_nothing:} is used to mark the end of a fast
% short-term recursion: the function \cs{__prg_break:n} uses this to
% break out of the loop.
% \end{function}
%
% \begin{function}[EXP]{\__prg_break:, \__prg_break:n}
% \begin{syntax}
% \cs{__prg_break:n} \Arg{code} \ldots{} \cs{__prg_break_point:}
% \end{syntax}
% Breaks a recursion which has no \meta{ending code} and which is not
% a user-breakable mapping (see for instance \cs{prop_get:Nn}), and
% inserts the \meta{code} in the input stream.
% \end{function}
%
% \end{documentation}
%
% \begin{implementation}
%
% \section{\pkg{l3prg} implementation}
%
% \TestFiles{m3prg001.lvt,m3prg002.lvt,m3prg003.lvt}
%
% \begin{macrocode}
%<*initex|package>
% \end{macrocode}
%
% \subsection{Primitive conditionals}
%
% \begin{macro}{\if_bool:N}
% \begin{macro}{\if_predicate:w}
% Those two primitive \TeX{} conditionals are synonyms.
% \begin{macrocode}
\cs_new_eq:NN \if_bool:N \tex_ifodd:D
\cs_new_eq:NN \if_predicate:w \tex_ifodd:D
% \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Defining a set of conditional functions}
%
% \begin{macro}
% {
% \prg_set_conditional:Npnn,
% \prg_new_conditional:Npnn,
% \prg_set_protected_conditional:Npnn,
% \prg_new_protected_conditional:Npnn
% }
% \begin{macro}
% {
% \prg_set_conditional:Nnn,
% \prg_new_conditional:Nnn,
% \prg_set_protected_conditional:Nnn,
% \prg_new_protected_conditional:Nnn
% }
% \begin{macro}{\prg_set_eq_conditional:NNn, \prg_new_eq_conditional:NNn}
% \begin{macro}{\prg_return_true:}
% \TestMissing
% {This function is implicitly tested with all other conditionals!}
% \begin{macro}{\prg_return_false:}
% \TestMissing
% {This function is also implicitly tested with all other conditionals!}
% These are all defined in \pkg{l3basics}, as they are needed
% \enquote{early}. This is just a reminder!
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \subsection{The boolean data type}
%
% \begin{macrocode}
%<@@=bool>
% \end{macrocode}
%
% \begin{macro}{\bool_new:N, \bool_new:c}
% \UnitTested
% Boolean variables have to be initiated when they are created. Other
% than that there is not much to say here.
% \begin{macrocode}
\cs_new_protected:Npn \bool_new:N #1 { \cs_new_eq:NN #1 \c_false_bool }
\cs_generate_variant:Nn \bool_new:N { c }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}
% {
% \bool_set_true:N, \bool_set_true:c,
% \bool_gset_true:N, \bool_gset_true:c,
% \bool_set_false:N, \bool_set_false:c,
% \bool_gset_false:N, \bool_gset_false:c
% }
% \UnitTested
% Setting is already pretty easy.
% When \texttt{check-declarations} is active, the definitions are patched to
% make sure the boolean exists. This is needed because booleans are
% not based on token lists nor on \TeX{} registers.
% \begin{macrocode}
\__kernel_patch:nnNNpn { \__kernel_chk_var_local:N #1 } { }
\cs_new_protected:Npn \bool_set_true:N #1
{ \cs_set_eq:NN #1 \c_true_bool }
\__kernel_patch:nnNNpn { \__kernel_chk_var_local:N #1 } { }
\cs_new_protected:Npn \bool_set_false:N #1
{ \cs_set_eq:NN #1 \c_false_bool }
\__kernel_patch:nnNNpn { \__kernel_chk_var_global:N #1 } { }
\cs_new_protected:Npn \bool_gset_true:N #1
{ \cs_gset_eq:NN #1 \c_true_bool }
\__kernel_patch:nnNNpn { \__kernel_chk_var_global:N #1 } { }
\cs_new_protected:Npn \bool_gset_false:N #1
{ \cs_gset_eq:NN #1 \c_false_bool }
\cs_generate_variant:Nn \bool_set_true:N { c }
\cs_generate_variant:Nn \bool_set_false:N { c }
\cs_generate_variant:Nn \bool_gset_true:N { c }
\cs_generate_variant:Nn \bool_gset_false:N { c }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}
% {
% \bool_set_eq:NN, \bool_set_eq:cN,
% \bool_set_eq:Nc, \bool_set_eq:cc,
% \bool_gset_eq:NN, \bool_gset_eq:cN,
% \bool_gset_eq:Nc, \bool_gset_eq:cc
% }
% \UnitTested
% The usual copy code. While it would be cleaner semantically to copy
% the \cs{cs_set_eq:NN} family of functions, we copy \cs{tl_set_eq:NN}
% because that has the correct checking code.
% \begin{macrocode}
\cs_new_eq:NN \bool_set_eq:NN \tl_set_eq:NN
\cs_new_eq:NN \bool_gset_eq:NN \tl_gset_eq:NN
\cs_generate_variant:Nn \bool_set_eq:NN { Nc, cN, cc }
\cs_generate_variant:Nn \bool_gset_eq:NN { Nc, cN, cc }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\bool_set:Nn, \bool_set:cn}
% \begin{macro}{\bool_gset:Nn, \bool_gset:cn}
% This function evaluates a boolean expression and assigns the first
% argument the meaning \cs{c_true_bool} or \cs{c_false_bool}.
% Again, we include some checking code.
% \begin{macrocode}
\__kernel_patch:nnNNpn { \__kernel_chk_var_local:N #1 } { }
\cs_new_protected:Npn \bool_set:Nn #1#2
{ \tex_chardef:D #1 = \bool_if_p:n {#2} }
\__kernel_patch:nnNNpn { \__kernel_chk_var_global:N #1 } { }
\cs_new_protected:Npn \bool_gset:Nn #1#2
{ \tex_global:D \tex_chardef:D #1 = \bool_if_p:n {#2} }
\cs_generate_variant:Nn \bool_set:Nn { c }
\cs_generate_variant:Nn \bool_gset:Nn { c }
% \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}[pTF]{\bool_if:N, \bool_if:c}
% \UnitTested
% Straight forward here. We could optimize here if we wanted to as
% the boolean can just be input directly.
% \begin{macrocode}
\prg_new_conditional:Npnn \bool_if:N #1 { p , T , F , TF }
{
\if_bool:N #1
\prg_return_true:
\else:
\prg_return_false:
\fi:
}
\prg_generate_conditional_variant:Nnn \bool_if:N { c } { p , T , F , TF }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\bool_show:n, \bool_log:n}
% \begin{macro}{\@@_to_str:n}
% Show the truth value of the boolean, as \texttt{true} or
% \texttt{false}.
% \begin{macrocode}
\cs_new_protected:Npn \bool_show:n
{ \msg_show_eval:Nn \@@_to_str:n }
\cs_new_protected:Npn \bool_log:n
{ \msg_log_eval:Nn \@@_to_str:n }
\cs_new:Npn \@@_to_str:n #1
{ \bool_if:nTF {#1} { true } { false } }
% \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\bool_show:N, \bool_show:c, \bool_log:N, \bool_log:c, \@@_show:NN}
% Show the truth value of the boolean, as \texttt{true} or
% \texttt{false}.
% \begin{macrocode}
\cs_new_protected:Npn \bool_show:N { \@@_show:NN \tl_show:n }
\cs_generate_variant:Nn \bool_show:N { c }
\cs_new_protected:Npn \bool_log:N { \@@_show:NN \tl_log:n }
\cs_generate_variant:Nn \bool_log:N { c }
\cs_new_protected:Npn \@@_show:NN #1#2
{
\__kernel_check_defined:NT #2
{ \exp_args:Nx #1 { \token_to_str:N #2 = \@@_to_str:n {#2} } }
}
% \end{macrocode}
% \end{macro}
%
% \begin{variable}{\l_tmpa_bool, \l_tmpb_bool, \g_tmpa_bool, \g_tmpb_bool}
% A few booleans just if you need them.
% \begin{macrocode}
\bool_new:N \l_tmpa_bool
\bool_new:N \l_tmpb_bool
\bool_new:N \g_tmpa_bool
\bool_new:N \g_tmpb_bool
% \end{macrocode}
% \end{variable}
%
% \begin{macro}[pTF]{\bool_if_exist:N, \bool_if_exist:c}
% Copies of the \texttt{cs} functions defined in \pkg{l3basics}.
% \begin{macrocode}
\prg_new_eq_conditional:NNn \bool_if_exist:N \cs_if_exist:N
{ TF , T , F , p }
\prg_new_eq_conditional:NNn \bool_if_exist:c \cs_if_exist:c
{ TF , T , F , p }
% \end{macrocode}
% \end{macro}
%
% \subsection{Boolean expressions}
%
% \begin{macro}[pTF]{\bool_if:n}
% \UnitTested
% Evaluating the truth value of a list of predicates is done using an
% input syntax somewhat similar to the one found in other programming
% languages with |(| and |)| for grouping, |!| for logical
% \enquote{Not}, |&&| for logical \enquote{And} and \verb"||" for
% logical \enquote{Or}. However, they perform eager evaluation.
% We shall use the terms Not, And, Or, Open and
% Close for these operations.
%
% Any expression is terminated by a Close operation. Evaluation
% happens from left to right in the following manner using a GetNext
% function:
% \begin{itemize}
% \item If an Open is seen, start evaluating a new expression using
% the Eval function and call GetNext again.
% \item If a Not is seen, remove the |!| and call a GetNext
% function with the logic reversed.
% \item If none of the above, reinsert the token found (this is
% supposed to be a predicate function) in front of an Eval
% function, which evaluates it to the boolean value \meta{true} or
% \meta{false}.
% \end{itemize}
% The Eval function then contains a post-processing operation which
% grabs the instruction following the predicate. This is either And,
% Or or Close. In each case the truth value is used to determine
% where to go next. The following situations can arise:
% \begin{description}
% \item[\meta{true}And] Current truth value is true, logical And
% seen, continue with GetNext to examine truth value of next
% boolean (sub-)expression.
% \item[\meta{false}And] Current truth value is false, logical And
% seen, stop using the values of predicates within this
% sub-expression until the next Close. Then return \meta{false}.
% \item[\meta{true}Or] Current truth value is true, logical Or seen,
% stop using the values of predicates within this sub-expression
% until the nearest Close. Then return \meta{true}.
% \item[\meta{false}Or] Current truth value is false, logical Or
% seen, continue with GetNext to examine truth value of next
% boolean (sub-)expression.
% \item[\meta{true}Close] Current truth value is true, Close
% seen, return \meta{true}.
% \item[\meta{false}Close] Current truth value is false, Close
% seen, return \meta{false}.
% \end{description}
% \begin{macrocode}
\prg_new_conditional:Npnn \bool_if:n #1 { T , F , TF }
{
\if_predicate:w \bool_if_p:n {#1}
\prg_return_true:
\else:
\prg_return_false:
\fi: