retroforth/doc/papers/Notes_on_the_Kernel_Wordset.txt

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In implementing the Retro 12 kernel (called Rx) I had to decide
on what functionality would be needed. It was important to me
that this be kept clean and minimalistic, as I didn't want to
spend a lot of time changing it as time progressed. It's far
nicer to code at the higher level, where the Retro language is
functional, as opposed to writing more assembly code.
So what made it in?
Primitives
These are words that map directly to Nga instructions.
dup drop swap call eq? -eq? lt? gt?
fetch store + - * /mod and or
xor shift push pop 0;
Memory
fetch-next store-next , s,
Strings
s:to-number s:eq? s:length
Flow Control
choose if -if repeat again
Compiler & Interpreter
Compiler Heap ; [ ] Dictionary
d:link d:class d:xt d:name d:add-header
class:word class:primitive class:data class:macro
prefix:: prefix:# prefix:& prefix:$
interpret d:lookup err:notfound
I *could* slightly reduce this. The $ prefix could be defined in
higher level code, and I don't strictly *need* to expose the
`fetch-next` and `store-next` here. But since the are already
implemented as dependencies of the words in the kernel, it would
be a bit wasteful to redefine them later in higher level code.
With these words the rest of the language can be built up. Note
that the Rx kernel does not provide any I/O words. It's assumed
that the Retro interfaces will add these as best suited for the
systems they run on.
There is another small bit. All images start with a few key
pointers in fixed offsets of memory. These are:
| Offset | Contains |
| ------ | --------------------------- |
| 0 | lit call nop nop |
| 1 | Pointer to main entry point |
| 2 | Dictionary |
| 3 | Heap |
| 4 | Retro version identifier |
An interface can use the dictionary pointer and knowledge of the
dictionary format for a specific Retro version to identify the
location of essential words like `interpret` and `err:notfound`
when implementing the user facing interface.