algorithmsenvironments
I would like to add a new command to an existing environment. The \renewenvironment command does not help a lot since I need to copy and paste the entire environment definition.
For an example I would like to make a \FORALL_P for the algorithmic environment such that instead of producing
forall ... do
as original \FORALL, it produces
forall ... do in parallel
Here is a modification added to algorithmic that allows you to \BREAK and have an annotated loop \ALOOP (and \ENDALOOP). It is based on a copy of the regular \LOOP and \ENDLOOP combinations, with an added parameter for annotation. Of course, more modifications are possible:
\documentclass{article}
\usepackage{algorithm,algorithmic}% http://ctan.org/pkg/algorithms
% Algorithmic modifications
\makeatletter
\newcommand{\ALOOP}[1]{\ALC@it\algorithmicloop\ #1%
\begin{ALC@loop}}
\newcommand{\ENDALOOP}{\end{ALC@loop}\ALC@it\algorithmicendloop}
\renewcommand{\algorithmicrequire}{\textbf{Input:}}
\renewcommand{\algorithmicensure}{\textbf{Output:}}
\newcommand{\algorithmicbreak}{\textbf{break}}
\newcommand{\BREAK}{\STATE \algorithmicbreak}
\makeatother
\begin{document}
\begin{algorithm}
\caption{My-Algorithm}\label{algo:blah}
\begin{algorithmic}[1]
\show\LOOP
\REQUIRE X
\ENSURE Y
% STEP 1
\STATE \COMMENT{\textbf{Step 1}} some something
\ALOOP {outer} % Outer loop
% STEP 2
\STATE \COMMENT{\textbf{Step 2}} do something more
\IF {$a = b$}
\RETURN $c$
\ELSE
\ALOOP {inner} % Inner loop
% STEP 3
\STATE \COMMENT{\textbf{Step 3}} do some more
\IF {$b = c$}
\STATE $y = x$
\BREAK % intending to break
\ELSE
% STEP 4
\STATE \COMMENT{\textbf{Step 4}} and yet some more
\ENDIF
\ENDALOOP
\ENDIF
\ENDALOOP
\end{algorithmic}
\end{algorithm}
\end{document}
It would also be possible to modify \BREAK to take an argument if you want to annotate that as well (like breaking out of a specific loop, say).
For completeness, I've fixed your use of \bf. As such, see Does it matter if I use \textit or \it, \bfseries or \bf, etc. and Will two-letter font style commands (\bf, \it, …) ever be resurrected in LaTeX?
I fudged it with a \trlap from stackengine package. EDITED to add listparindent specifier.
\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[francais]{babel}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{enumitem}
\usepackage{lipsum}
\usepackage{stackengine}
\renewlist{cases}{enumerate}{10}
\setlist[cases]{label=%
\trlap{\textbf{\kern5pt Cas \arabic* :}}, itemindent=0pt,leftmargin=0pt,
listparindent=1.5em}
\begin{document}
\begin{cases}
\item \lipsum[1]
\lipsum[4]
\item \lipsum[4]
\end{cases}
\end{document}
Best Answer
You can say
The definition of
\FORALLPis modeled on that of\FORALL; you can't call it\FORALL_P, however.