Package org.scijava.script

Class DefaultScriptInterpreter

java.lang.Object

org.scijava.script.DefaultScriptInterpreter

All Implemented Interfaces:

ScriptInterpreter

public class DefaultScriptInterpreter
extends Object
implements ScriptInterpreter

The default implementation of a ScriptInterpreter.

Credit to Jason Sachs for the multi-line evaluation (see his post on StackOverflow).

Author:

Johannes Schindelin, Curtis Rueden

Field Summary

Fields inherited from interface org.scijava.script.ScriptInterpreter

MORE_INPUT_PENDING

Constructor Summary

Constructors

Constructor	Description
DefaultScriptInterpreter(PrefService prefs, ScriptService scriptService, ScriptLanguage language)	Deprecated. Use DefaultScriptInterpreter(ScriptLanguage) instead.
DefaultScriptInterpreter(ScriptLanguage language)	Creates a new script interpreter for the given script language.
DefaultScriptInterpreter(ScriptLanguage language, ScriptEngine engine)	Creates a new script interpreter for the given script language, using the specified script engine.

Method Summary

Modifier and Type	Method	Description
Object	eval(String command)	Evaluates a command.
Bindings	getBindings()	Returns the Bindings of the associated ScriptEngine at ScriptContext.ENGINE_SCOPE scope.
ScriptEngine	getEngine()	Returns the associated ScriptEngine.
ScriptLanguage	getLanguage()	Returns the associated ScriptLanguage.
Object	interpret(String line)	Interprets the given line of code, which might be part of a multi-line statement.
boolean	isExpectingMoreInput()
boolean	isReady()
void	readHistory()	Reads the persisted history of the current script interpreter.
void	reset()	Clears the buffer of not-yet-evaluated lines of code, accumulated from previous calls to ScriptInterpreter.interpret(java.lang.String).
String	walkHistory(String currentCommand, boolean forward)	Obtains the next/previous command in the command history.
void	writeHistory()	Persists the history of the current script interpreter.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DefaultScriptInterpreter

@Deprecated
public DefaultScriptInterpreter(PrefService prefs,
                                ScriptService scriptService,
                                ScriptLanguage language)

Deprecated.

Use DefaultScriptInterpreter(ScriptLanguage) instead.

DefaultScriptInterpreter

public DefaultScriptInterpreter(ScriptLanguage language)

Creates a new script interpreter for the given script language.

Parameters:

language - ScriptLanguage of the interpreter

DefaultScriptInterpreter

public DefaultScriptInterpreter(ScriptLanguage language,
                                ScriptEngine engine)

Creates a new script interpreter for the given script language, using the specified script engine.

Parameters:

language - ScriptLanguage of the interpreter

engine - ScriptEngine to use, or null for the specified language's default engine

Method Detail

readHistory

public void readHistory()

Description copied from interface: ScriptInterpreter

Reads the persisted history of the current script interpreter.

Specified by:

readHistory in interface ScriptInterpreter

writeHistory

public void writeHistory()

Description copied from interface: ScriptInterpreter

Persists the history of the current script interpreter.

Specified by:

writeHistory in interface ScriptInterpreter

walkHistory

public String walkHistory(String currentCommand,
                          boolean forward)

Description copied from interface: ScriptInterpreter

Obtains the next/previous command in the command history.

Specified by:

walkHistory in interface ScriptInterpreter

Parameters:

currentCommand - the current command (will be stored in the history)

forward - if true, the next history entry is returned (more recent), if false, the previous one

Returns:

the next/previous command

eval

public Object eval(String command)
            throws ScriptException

Description copied from interface: ScriptInterpreter

Evaluates a command.

Specified by:

eval in interface ScriptInterpreter

Parameters:

command - the command to evaluate

Returns:

result of the evaluation

Throws:

ScriptException

interpret

public Object interpret(String line)
                 throws ScriptException

Interprets the given line of code, which might be part of a multi-line statement.

This implementation from Jason Sachs uses the following strategy:

• Keep a pending list of input lines not yet evaluated.
• Try compiling (but not evaluating) the pending input lines.
  • If the compilation is OK, we may be able to execute pending input lines.
  • If the compilation throws an exception, and there is an indication of the position (line + column number) of the error, and this matches the end of the pending input, then that's a clue that we're expecting more input, so swallow the exception and wait for the next line.
  • Otherwise, we either don't know where the error is, or it happened prior to the end of the pending input, so rethrow the exception.
• If we are not expecting any more input lines, and we only have one line of pending input, then evaluate it and restart.
• If we are not expecting any more input lines, and the last one is a blank one, and we have more than one line of pending input, then evaluate it and restart. Python's interactive shell seems to do this.
• Otherwise, keep reading input lines.

This helps avoid certain problems:

• users getting annoyed having to enter extra blank lines after single-line inputs
• users entering a long multi-line statement and only find out after the fact that there was a syntax error in the 2nd line.

For further details, see SO #5584674.

Specified by:

interpret in interface ScriptInterpreter

Parameters:

line - line of code to interpret

Returns:

value of the line, or ScriptInterpreter.MORE_INPUT_PENDING if there is still pending input

Throws:

ScriptException - in case of an exception

reset

public void reset()

Description copied from interface: ScriptInterpreter

Clears the buffer of not-yet-evaluated lines of code, accumulated from previous calls to ScriptInterpreter.interpret(java.lang.String). In other words: start over with a new (potentially multi-line) statement, discarding the current partial one.

Specified by:

reset in interface ScriptInterpreter

See Also:

ScriptInterpreter.interpret(java.lang.String)

getLanguage

public ScriptLanguage getLanguage()

Description copied from interface: ScriptInterpreter

Returns the associated ScriptLanguage.

Specified by:

getLanguage in interface ScriptInterpreter

getEngine

public ScriptEngine getEngine()

Description copied from interface: ScriptInterpreter

Returns the associated ScriptEngine.

Specified by:

getEngine in interface ScriptInterpreter

Returns:

the script engine

getBindings

public Bindings getBindings()

Description copied from interface: ScriptInterpreter

Returns the Bindings of the associated ScriptEngine at ScriptContext.ENGINE_SCOPE scope.

Specified by:

getBindings in interface ScriptInterpreter

isReady

public boolean isReady()

Specified by:

isReady in interface ScriptInterpreter

Returns:

whether the interpreter is ready for a brand new statement.

See Also:

ScriptInterpreter.interpret(String)

isExpectingMoreInput

public boolean isExpectingMoreInput()

Specified by:

isExpectingMoreInput in interface ScriptInterpreter

Returns:

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 Also:

ScriptInterpreter.interpret(String)