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Application developers can create new application-specific data types, and methods that enable those data types to be used by both Scheme programs and
C++ functions.
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Methods include the following:
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Constructor
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creates an instance of the type (not required).
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Destructor
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deletes an instance of the type (not required).
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init
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initializes the type. It calls
Define_Type to actually define the type to Scheme. It is invoked using the
SCM_INIT macro.
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Equal
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compares two instances of the type to determine if they are the same. Call the debug macro,
ENTER_FUNCTION(method_name), at the beginning of the function. This method is supplied to
Define_Type for the interpreter's use.
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Print
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prints an instance of the type. Call the debug macro,
ENTER_FUNCTION(method_name), at the beginning of the function. This method is supplied to
Define_Type for the interpreter's use.
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Is
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determines if a Scheme object is of this particular type. Call the debug macro,
ENTER_FUNCTION(method_name), at the beginning of the function.
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Get
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creates aC++ object of this type of Scheme object. Call the debug macro,
ENTER_FUNCTION(method_name), at the beginning of the function.
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Make
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creates a Scheme object of this type from a
C++ object. Call the debug macro,
ENTER_FUNCTION(method_name), at the beginning of the function.
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The following sections analyze the
GC_BndCrv class and its methods as an example of how to derive a new data type. GC is an acronym for garbage collection, which is the process of recovering and reusing memory allocated by the
Scheme Interpreter. The interpreter never destroys a Scheme object unless it can prove that the object is not used again. It does, however, recycle memory efficiently to prevent excessive memory allocation.
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