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We can access the internal representation of all the compound Scheme values implemented as “blocks” with the following system operations.
Unsafe slot getter. We can use it when we know that: ?block-value is a reference to a block value; ?slot-index is a valid slot index for ?block-value. Return the undefined value.
Unsafe slot setter. We can use it when we know that: ?block-value is a reference to a block value; ?slot-index is a valid slot index for ?block-value. Return the undefined value.
Like ##sys#setslot, it is an unsafe slot setter with an additional constraint on the new
value. We can use it when we know that: ?block-value is a reference to a block value;
?slot-index is a valid slot index for ?block-value; ?new-immediate-value is any
immediate Scheme value (examples: a fixnum, a boolean). Return the undefined value.
NOTE No validation is performed against ?new-immediate-value to check that it is actually an immediate value.
Unsafe block length getter: return a fixnum representing the number of slots. We can use it when we know that: ?block-value is a reference to a block value.
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