38 lines
1.2 KiB
Ruby
38 lines
1.2 KiB
Ruby
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# this is not a "normal" ruby file, ie it is not required by salama
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# instead it is parsed by salama to define part of the program that runs
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# Values are _not_ objects. Specifically they have the following properties not found in objects:
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# - they are immutable
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# - equality implies identity == is ===
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# - they have type, not class
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# To make them useful in an oo system, we assign a class to each basic type
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# This makes them look more like objects, but they are not.
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# Value is an abstract class that unifies the "has a type" concept
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# Types are not "objectified", but are represented as integer constants
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class Value
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# to make the machine work, the constants need
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# - to start at 0
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# - be unique
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# - be smaller enough to fit into the 2-4 bits available
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INTEGER_VALUE = 0
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OBJECT_VALUE = 1
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# the type is what identifies the value
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def get_type()
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raise "abstract clalled on #{self}"
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end
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# Get class works on the type. The value's type is stored by the machine.
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# So this function is not overriden in derived classes, because it is used
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# to espablish what class a value has! (it's that "fake" oo i mentioned)
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def get_class()
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type = self.get_type()
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return Integer if( type == INTEGER_VALUE )
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raise "invalid type"
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end
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end
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