slogo.instruction

Class If

java.lang.Object

slogo.GrammarElement

slogo.instruction.Instruction

slogo.instruction.If

public class If
extends Instruction

An IF instruction has two components: (1) an expression representing the varOrComman and (2) a strict instruction list that is the list of instructions that will be executed.

To evaluate an IF instruction the expression is evaluated first, this determines if the instruction list will be run or not. This instruction list is executed the appropriate number of times the expression is not 0.

The value returned by evaluating an IF instruction is the expression and the instruction list.

Field Summary

Fields

Modifier and Type	Field and Description
private StrictInstructionList	instructionList
private ArithmeticBase	varOrCommand

Fields inherited from class slogo.GrammarElement

gelementsToValue

Constructor Summary

Constructors

Constructor and Description
If(ArithmeticBase e, StrictInstructionList sil) Constructs a Repeat 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

varOrCommand

private ArithmeticBase varOrCommand

instructionList

private StrictInstructionList instructionList

Constructor Detail

If

public If(ArithmeticBase e,
          StrictInstructionList sil)

Constructs a Repeat instruction that can be executed.

Parameters:

e - number to determine if the list should run

sil - strict instruction list that is the body

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 result of evaluating the instruction list the last time

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

Returns:

a String representing this instruction as IF, followed by the expression about the VarOrCommand and the list of instructions