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\section{library(readline): GNU readline interface}

\label{sec:readline}

\begin{tags}
    \tag{license}
Although the interface is BSD-licensed, the GNU readline
library itself is covered by the GPL (General Public License). This
implies that loading this library in an application makes all code
loaded into the application subject to the GPL conditions.
\end{tags}

This library binds GNU libreadline to SWI-Prolog. The GNU readline
library provides emacs and vi based editing of queries on the Prolog
toplevel, including TAB-based completion and history.

This library is by default loaded into an interactive Prolog process
that is connected to a (Unix) terminal. Loading can be stopped by
setting the Prolog flag \const{readline} to \const{false}.\vspace{0.7cm}

\begin{description}
    \predicate[det]{rl_read_init_file}{1}{+File}
Read a GNU readline config file. See the GNU readline manual for
details.

    \predicate[det]{rl_add_history}{1}{+Line}
Add a line to the history.

    \predicate[det]{rl_write_history}{1}{+File}
Save the history to \arg{File}. This can be reloaded in a next session
using \predref{rl_read_history}{1}.

    \predicate[det]{rl_read_history}{1}{+File}
Read a saved history from \arg{File}.
\end{description}