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