Class Interval Collection lower upper step
Methods Interval

	step: aValue
		step <- aValue

]
Methods Interval

	lower: aValue
		lower <- aValue

]
Methods Interval
	do: aBlock		| current |
		current <- lower.
		(step > 0) 
			ifTrue: [ [ current <= upper ] whileTrue:
					[ aBlock value: current.
			  		current <- current + step ] ]
			ifFalse: [ [ current >= upper ] whileTrue:
					[ aBlock value: current.
					current <- current + step ] ]

]
Methods Interval

	upper: aValue
		upper <- aValue

]