ix.util.lisp
Class Interpreter

java.lang.Object
  ix.util.lisp.Interpreter

Direct Known Subclasses:

LispInterpreter

public abstract class Interpreter
extends java.lang.Object

The skeleton of a progamming language interpreter. This class implements a language that is semantically similar to a simple version of Scheme without continuations. However, it doesn't provide any syntax or built-in functions. It is expected that they will be provided by a subclass. The subclass should produce Expr objects from whatever surface syntax it desires. There are Expr classes for constants (literals), variable references, conditional expressions, and so on. Functions should implement the Function interface. Usually they will extend the JFunction class.

Nested Class Summary

protected class	Interpreter.AbstractEnv An implementation of Env that supplies some utility methods.
static class	Interpreter.AbstractFunction An implementation of Function that supplies some utility methods and implements part of the interface.
static class	Interpreter.And A conditional AND.
static class	Interpreter.Assignment An assignment to a variable.
static class	Interpreter.Call A function call.
static class	Interpreter.Closure An interpreted function.
static interface	Interpreter.Env The context in which an expression is evaluated.
static class	Interpreter.Error The root class for exceptions thrown for error conditions detected by an Interpreter or by an expression.
static class	Interpreter.Expr The root class for expressions.
static interface	Interpreter.Function An object that represents a function that can be applied to arguments.
class	Interpreter.GlobalEnv A global / top-level environment.
static class	Interpreter.If A simple conditional expression.
static class	Interpreter.JFunction A function implemented in Java.
static class	Interpreter.Lambda An expression whose value is a function closed in the environment in which this Lambda is evaluated.
static class	Interpreter.Let An expression that binds variables and then evaluates an expression in the resulting environment.
class	Interpreter.LexicalEnv An environment for local values of variables.
static class	Interpreter.Literal A reference to an object that is treated as a literal.
static class	Interpreter.Or A conditional OR.
static class	Interpreter.Sequence A sequence of expressions.
static class	Interpreter.VarRef A reference to a variable.
static class	Interpreter.While A while loop.

Field Summary

protected boolean	acceptOnlySafeBuiltins Controls whether only safe builtin functions are added.
protected java.lang.Object	DEFAULT The value this interpreter thinks expressions should return when they cannot determine any more appropriate value.
protected static java.lang.Object	FALSE The value that an interpreter thinks should be used by default to represent falsity.
protected Interpreter.GlobalEnv	globalEnv This interpreter's global / top-level environment.
protected static IScript	iscript An IScript factory used when constructing external forms.
protected static java.lang.Object	TRUE The value that an interpreter thinks should be used by default to represent truth.

Constructor Summary

Interpreter()
Constructs an interpreter.

Method Summary

boolean	isSafe() Says whether the interpreter can safely be used in cases where you don't want the user to be able to do such things as call arbitrary Java methods, read or write files, or get other information about the host machine.
boolean	isTrue(java.lang.Object obj) Determines whether this interpreter regards the object as true; otherwise, the object is considered false.
protected static java.lang.String	nameForClass(java.lang.Class c) A utility that returns a relatively readable name for a class.
java.lang.Object	topLevelApply(java.lang.Object function, java.lang.Object[] args) Applies the function to the specified arguments.
java.lang.Object	topLevelEval(Interpreter.Expr e) Evaluates the expression in the top-level enviromnent of this interpreter.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT

protected java.lang.Object DEFAULT

The value this interpreter thinks expressions should return when they cannot determine any more appropriate value.

TRUE

protected static java.lang.Object TRUE

The value that an interpreter thinks should be used by default to represent truth. It is the same as Boolean.TRUE.

FALSE

protected static java.lang.Object FALSE

The value that an interpreter thinks should be used by default to represent falsity. It is the same as Boolean.FALSE.

globalEnv

protected Interpreter.GlobalEnv globalEnv

This interpreter's global / top-level environment.

iscript

protected static IScript iscript

An IScript factory used when constructing external forms.

acceptOnlySafeBuiltins

protected boolean acceptOnlySafeBuiltins

Controls whether only safe builtin functions are added. To make a safe interpreter, this field must be set to true before any JFunction is added.

See Also:

isSafe()

Constructor Detail

Interpreter

public Interpreter()

Constructs an interpreter.

Method Detail

isTrue

public boolean isTrue(java.lang.Object obj)

Determines whether this interpreter regards the object as true; otherwise, the object is considered false.

Note that expressions do not call this method directly. Instead, they must call the Interpreter.Env.isTrue(Object) method of an environment.

topLevelEval

public java.lang.Object topLevelEval(Interpreter.Expr e)

Evaluates the expression in the top-level enviromnent of this interpreter.

topLevelApply

public java.lang.Object topLevelApply(java.lang.Object function,
                                      java.lang.Object[] args)

Applies the function to the specified arguments. Note that the function may be given as a name (Symbol) rather than as an instance of Interpreter.Function. If so, the name is looked up in the top-level environment of this interpreter.

isSafe

public boolean isSafe()

Says whether the interpreter can safely be used in cases where you don't want the user to be able to do such things as call arbitrary Java methods, read or write files, or get other information about the host machine. Interpreters are unsafe by default.

See Also:

acceptOnlySafeBuiltins, LispInterpreter.LispInterpreter(boolean beSafe)

nameForClass

protected static java.lang.String nameForClass(java.lang.Class c)

A utility that returns a relatively readable name for a class.