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\section{library(snowball): The Snowball multi-lingual stemmer library}

\label{sec:snowball}

\begin{tags}
    \tag{See also}
\url{http://snowball.tartarus.org/}
\end{tags}

This module encapsulates "The C version of the libstemmer library" from
the Snowball project. This library provides stemmers in a variety of
languages. The interface to this library is very simple:

\begin{itemize}
    \item \predref{snowball}{3} stems a word with a given algorithm
    \item \predref{snowball_current_algorithm}{1} enumerates the provided algorithms.
\end{itemize}

Here is an example:

\begin{code}
?- snowball(english, walking, S).
S = walk.
\end{code}

\vspace{0.7cm}

\begin{description}
    \predicate[det]{snowball}{3}{+Algorithm, +Input, -Stem}
Apply the Snowball \arg{Algorithm} on \arg{Input} and unify the result
(an atom) with \arg{Stem}.

The implementation maintains a cache of stemmers for each thread
that accesses \predref{snowball}{3}, providing high-perfomance and
thread-safety without locking.

\begin{arguments}
\arg{Algorithm} & is the (english) name for desired algorithm
or an 2 or 3 letter ISO 639 language code. \\
\arg{Input} & is the word to be stemmed. It is either an
atom, string or list of chars/codes. The library
accepts Unicode characters. \arg{Input} must be
\textit{lowercase}. See \predref{downcase_atom}{2}. \\
\end{arguments}

\begin{tags}
\mtag{Errors}- \verb$domain_error(snowball_algorithm, Algorithm)$ \\- \verb$type_error(atom, Algorithm)$ \\- \verb$type_error(text, Input)$
\end{tags}

    \predicate[nondet]{snowball_current_algorithm}{1}{?Algorithm}
True if \arg{Algorithm} is the official name of an algorithm suported
by \predref{snowball}{3}. The predicate is \const{semidet} if \arg{Algorithm} is given.
\end{description}