slogo.instruction

Class If

java.lang.Object

slogo.GrammarElement

slogo.instruction.Instruction

slogo.instruction.If

public class If
extends Instruction

An AST (abstract syntax tree) for a SLogo REPEAT instruction. A REPEAT instruction has two components: (1) an expression representing the number of times to repeat the instructions that follow and (2) a strict instruction list that is the list of instructions that will be (repeatedly) executed.

To evaluate a REPEAT instruction the expression is evaluated first, this determines the number of times the instruction list is executed. This instruction list is executed the appropriate number of times.

The value returned by evaluating a REPEAT instruction is the last value returned by evaluating the instruction list.

Field Summary

Fields

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

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

expression

private ArithmeticBase expression

instructionList

private StrictInstructionList instructionList

Constructor Detail

If

public If(ArithmeticBase e,
          StrictInstructionList sil)

Constructs a Repeat instruction that can be executed.

Parameters:

e - number of times to repeat the body

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 REPEAT, followed by the expression about how many times to repeat the instructions and the list of instructions