\documentclass[10pt,a4paper]{article}

\usepackage{tikz}
\usepackage{arrayjob}

\usepackage[parfill]{parskip}

%%%
%%%
%%%
\newcommand{\slithergadget}[1]{
\newarray\names
\readarray{names}{#1}
\begin{tikzpicture}[scale=0.5]
  \foreach \i in {0,1,...,6}{
    \foreach \j in {0,1,...,6}{
      \node[outer sep=0pt, inner sep=0pt] (\i;\j) at (\i,6-\j) {$\bullet$};
    }
  }
  \foreach \i in {0,...,5}{
    \foreach \j in {0,...,5}{
      \node[] at (\i+0.5,5.35-\j) {\smash{\names(\the\numexpr 1+6*\j+\i \relax)}};
    }
  }
  \foreach \i in {0,...,5}{
    \foreach \j in {0,...,6}{
      \checknames(\the\numexpr 36+1+13*\j+\i \relax)
      \edef\myvar{-}
      \ifx\cachedata\myvar\relax
        \draw[-,thick] (\i;\j) -- (\the\numexpr \i+1 \relax;\j);
      \fi    
    }
  }
  \foreach \i in {0,...,6}{
    \foreach \j in {0,...,5}{
      \checknames(\the\numexpr 36+1+6+13*\j+\i \relax)
      \edef\myvar{|}
      \ifx\cachedata\myvar\relax
        \draw[-,thick] (\i;\j) -- (\i;\the\numexpr \j+1 \relax);
      \fi    
    }
  }
\end{tikzpicture}
}
%%%
%%%
%%%

\begin{document}

\section*{Slitherlink template}

This document contains a template for typesetting Slitherlink instances and solutions
(on a grid of 6 by 6).

The following code (together with the macro definition in the source of this document)
displays a 6 by 6 grid with all edges.
\begin{quote}
\begin{verbatim}
\slithergadget{%
1&2&3&4&5&6&%
7&8&9&10&11&12&%
13&14&15&16&17&18&%
19&20&21&22&23&24&%
25&26&27&28&29&30&%
31&32&33&34&35&36&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
}
\end{verbatim}
\end{quote}
That is, it will display:
\begin{center}
\slithergadget{%
%
1&2&3&4&5&6&%
7&8&9&10&11&12&%
13&14&15&16&17&18&%
19&20&21&22&23&24&%
25&26&27&28&29&30&%
31&32&33&34&35&36&%
%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
|&|&|&|&|&|&|&%
-&-&-&-&-&-&%
%
}
\end{center}

\clearpage

By replacing the numbers in the template
and by removing some of the occurrences of \texttt{-} and \texttt{|},
you can create Slitherlink instances and/or solutions
on the 6 by 6 grid---or, for example, partial solutions for larger instances
with a 6 by 6 subgrid.

For example the following code:
\begin{quote}
\begin{verbatim}
\slithergadget{%
0&0&0&0&0&0&%
0&0&0&0&0&0&%
 & & & & & &%
 & & & & & &%
0&0&0&0&0&0&%
0&0&0&0&0&0&%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
-&-&-&-&-&-&%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
}
\end{verbatim}
\end{quote}
displays the following:
\begin{center}
\slithergadget{%
%
0&0&0&0&0&0&%
0&0&0&0&0&0&%
 & & & & & &%
 & & & & & &%
0&0&0&0&0&0&%
0&0&0&0&0&0&%
%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
-&-&-&-&-&-&%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
 & & & & & & &%
 & & & & & &%
%
}
\end{center}

\end{document}  