slogo.instruction

Class Forward

java.lang.Object

slogo.GrammarElement

slogo.instruction.Instruction

slogo.instruction.Forward

public class Forward
extends Instruction

A FORWARD instruction has one component: a GrammarElement that represents the number of steps to take in the forward direction. To evaluate a FORWARD instruction the expression is evaluated first, this determines the double version of the number of steps to take. The integer version of this is used to actually move the turtle.

The value returned by evaluating a FORWARD instruction is the expression itself, representing the number of steps taken.

Field Summary

Fields

Modifier and Type	Field and Description
private GrammarElement	expression

Fields inherited from class slogo.GrammarElement

gelementsToValue

Constructor Summary

Constructors

Constructor and Description
Forward(GrammarElement e) Constructs a FORWARD instruction that can be executed.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	evaluate(Context c) Evaluate this instruction in a Context.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

expression

private GrammarElement expression

Constructor Detail

Forward

public Forward(GrammarElement e)

Constructs a FORWARD instruction that can be executed.

Parameters:

e - number of steps to take

Method Detail

evaluate

public java.lang.Object evaluate(Context c)

Evaluate this instruction in a Context.

Specified by:

evaluate in class Instruction

Parameters:

c - the Context for the evaluation

Returns:

the number of steps moved

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

Returns:

a String representing this instruction as FD, followed by the expression about how steps were taken