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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.

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/*
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 * SciJava Common shared library for SciJava software.
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 * Copyright (C) 2009 - 2016 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
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 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
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package org.scijava.script;

import javax.script.Bindings;
import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

/**
 * The contract for script interpreters.
 * 
 * @author Johannes Schindelin
 * @author Curtis Rueden
 */
public interface ScriptInterpreter {

	/**
	 * A special object returned by {@link #interpret(String)} when the
	 * interpreter is expecting additional input before finishing the evaluation.
	 */
	Object MORE_INPUT_PENDING = new Object();

	/**
	 * Reads the persisted history of the current script interpreter.
	 */
	void readHistory();

	/**
	 * Persists the history of the current script interpreter.
	 */
	void writeHistory();

	/**
	 * Obtains the next/previous command in the command history.
	 * 
	 * @param currentCommand the current command (will be stored in the history)
	 * @param forward if true, the next history entry is returned (more recent),
	 *          if false, the previous one
	 * @return the next/previous command
	 */
	String walkHistory(String currentCommand, boolean forward);

	/**
	 * Evaluates a command.
	 * 
	 * @param command the command to evaluate
	 * @return result of the evaluation
	 * @throws ScriptException
	 */
	Object eval(String command) throws ScriptException;

	/**
	 * Interprets the given line of code, which might be part of a multi-line
	 * statement.
	 * 
	 * @param line line of code to interpret
	 * @return value of the line, or {@link #MORE_INPUT_PENDING} if there is still
	 *         pending input
	 * @throws ScriptException in case of an exception
	 */
	Object interpret(String line) throws ScriptException;

	/**
	 * Clears the buffer of not-yet-evaluated lines of code, accumulated from
	 * previous calls to {@link #interpret}. In other words: start over with a new
	 * (potentially multi-line) statement, discarding the current partial one.
	 * 
	 * @see #interpret
	 */
	void reset();

	/**
	 * Returns the associated {@link ScriptLanguage}.
	 */
	ScriptLanguage getLanguage();

	/**
	 * Returns the associated {@link ScriptEngine}.
	 * 
	 * @return the script engine
	 */
	ScriptEngine getEngine();

	/**
	 * Returns the {@link Bindings} of the associated {@link ScriptEngine} at
	 * {@link ScriptContext#ENGINE_SCOPE} scope.
	 */
	Bindings getBindings();

	/**
	 * @return whether the interpreter is ready for a brand new statement.
	 * @see #interpret(String)
	 */
	boolean isReady();

	/**
	 * @return whether the interpreter expects more input. A true value means
	 *         there is definitely more input needed. A false value means no more
	 *         input is needed, but it may not yet be appropriate to evaluate all
	 *         the pending lines. (there's some ambiguity depending on the
	 *         language)
	 * @see #interpret(String)
	 */
	boolean isExpectingMoreInput();

}