ix.util.lisp
Class Interpreter.Expr

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

Direct Known Subclasses:

Interpreter.And, Interpreter.Call, Interpreter.If, Interpreter.Lambda, Interpreter.Let, Interpreter.Literal, Interpreter.Or, Interpreter.Sequence, Interpreter.VarRef, Interpreter.While

Enclosing class:

Interpreter

public abstract static class Interpreter.Expr
extends java.lang.Object

The root class for expressions. Expressions are able to evaluate themselves when given an environment. This is done by calling the expression's _evalIn(Interpreter.Env) method. However, evalIn(Interpreter.Env) should normally be called instead. It puts some debugging support around a call to _evalIn, primarily so that a backtrace will appear if an exception is thrown.

Expressions have a "description" object that is used by their toString() method. It's main purpose is to describe the expression in a backtrace.

Expressions also have an "external form". Unlike the description, it is not meant to be nicely readable by a user. Instead, it is a representation that can be understood by the reflection and XML utilities and can be input and output. Converting an external form back to an expression should produce an expression that is equivalent to the original.

The default external form for instances of subclasses of this class is an IScript expression, an instance of a subclass of Expression. There is a fairly direct correspondence between subclasses of that class and subclasses of this one.

Conversion to external form is done by calling the expression's externalForm() method. Coversion in the other direction is done by creating an IScriptParser and calling its parseExpression method.

This class also provides some utility methods.

Field Summary

protected java.lang.Object

description

Constructor Summary

Interpreter.Expr()

Method Summary

protected abstract java.lang.Object	_evalIn(Interpreter.Env env) Implements this expression's semantics.
protected java.lang.Object[]	evalArgs(Interpreter.Expr[] args, Interpreter.Env env) A utility for evaluating argument expressions.
java.lang.Object	evalIn(Interpreter.Env env) Provides public access to this expression's semantics.
abstract Expression	externalForm() Returns a representation of this expression that can be understood by the reflection and XML utilities.
protected static ix.iscript.ListOfExpression	externalForm(Interpreter.Expr[] exprs) A utility for converting an array of Interpreter.Exprs to a List of their external forms.
protected static Interpreter.Expr[]	makeExprArray(java.util.List exprList) A utility for converting a List of Interpreter.Exprs to an array.
protected static Symbol[]	makeVarArray(java.util.List varList) A utility for converting a List of variables (Symbols) to an array.
void	setDescription(java.lang.Object d)
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

description

protected java.lang.Object description

Constructor Detail

Interpreter.Expr

public Interpreter.Expr()

Method Detail

_evalIn

protected abstract java.lang.Object _evalIn(Interpreter.Env env)

Implements this expression's semantics.

Note that this method is usually not called directly. Instead, call evalIn(Interpreter.Env).

externalForm

public abstract Expression externalForm()

Returns a representation of this expression that can be understood by the reflection and XML utilities.

See Also:

IScript

setDescription

public void setDescription(java.lang.Object d)

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

evalIn

public java.lang.Object evalIn(Interpreter.Env env)

Provides public access to this expression's semantics. This method typically wraps some debugging support around a call to _evalIn(Interpreter.Env).

evalArgs

protected java.lang.Object[] evalArgs(Interpreter.Expr[] args,
                                      Interpreter.Env env)

A utility for evaluating argument expressions.

makeExprArray

protected static Interpreter.Expr[] makeExprArray(java.util.List exprList)

A utility for converting a List of Interpreter.Exprs to an array.

makeVarArray

protected static Symbol[] makeVarArray(java.util.List varList)

A utility for converting a List of variables (Symbols) to an array.

externalForm

protected static ix.iscript.ListOfExpression externalForm(Interpreter.Expr[] exprs)

A utility for converting an array of Interpreter.Exprs to a List of their external forms.