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- == How are scheme values represented in C? ==
- There are simple "immediate" data types like booleans and numbers. They are self contained and can be built like this:
- #define SDBOOL(t) (sdata){.tag = tbool, .value = t}
- #define SDNUMB(t) (sdata){.tag = tnumb, .ivalue = t}
- Then there are symbols which are sort of like a mid-way between immediate and complex data that requires allocation. We "intern" symbol names into a symbol table. That enables us to reference a long complicated symbol name just using one integer.
- You might intern("x"), intern("y") then {.tag = tsymb, .value = 0} would represent 'x and {.tag = tsymb, .value = 1} would represent 'y.
- A similar but a more general structure is the heap which is just scratch space for any number of data. When we allocate a cons cell we ask for 2 spaces in the heap. For example we might end up with {.tag = tcons, .value = 325} which means that the car is at place 325 and the cdr is at place 326 of the heap.
- Vectors work in a similar way but they reserve 1 + length slots in the heap, first to store their length then to store their elements.
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