2021-01-21 13:40:28 +01:00
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</head><body>
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<p><span class="h2">On The Kernel Wordset</span>
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<br/><br/>
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2021-05-17 19:04:42 +02:00
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In implementing the Retro 12 kernel (called Retro Core, and
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2021-01-21 13:40:28 +01:00
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defined in <span class="tt">image/retro.muri</span>) I had to decide on what functionality
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would be needed. It was important to me that this be kept clean
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and minimalistic, as I didn't want to spend a lot of time
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changing it as time progressed. It's far nicer to code at the
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2021-05-17 19:04:42 +02:00
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higher level, where the Retro language is fully functional, as
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opposed to writing more assembly code.
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<br/><br/>
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So what made it in?
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<br/><br/>
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Primitives
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<br/><br/>
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These are words that map directly to Nga instructions.
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<br/><br/>
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<tt class='indentedcode'>dup drop swap call eq? -eq? lt? gt?</tt>
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<tt class='indentedcode'>fetch store + - * /mod and or</tt>
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<tt class='indentedcode'>xor shift push pop 0;</tt>
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<br/><br/>
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Memory
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<br/><br/>
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<tt class='indentedcode'>fetch-next store-next , s,</tt>
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<br/><br/>
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Strings
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<br/><br/>
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<tt class='indentedcode'>s:to-number s:eq? s:length</tt>
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<br/><br/>
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Flow Control
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<br/><br/>
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<tt class='indentedcode'>choose if -if repeat again</tt>
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<br/><br/>
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Compiler & Interpreter
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<br/><br/>
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<tt class='indentedcode'>Compiler Heap ; [ ] Dictionary</tt>
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<tt class='indentedcode'>d:link d:class d:xt d:name d:add-header</tt>
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<tt class='indentedcode'>class:word class:primitive class:data class:macro</tt>
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<tt class='indentedcode'>sigil:: sigil:# sigil:& sigil:$</tt>
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<tt class='indentedcode'>interpret d:lookup err:notfound</tt>
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<br/><br/>
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Assembler
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<br/><br/>
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<tt class='indentedcode'>i d r</tt>
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<br/><br/>
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2021-03-30 13:58:25 +02:00
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I <strong>could</strong> slightly reduce this. The $ sigil could be defined in
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2021-01-21 13:40:28 +01:00
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higher level code, and I don't strictly <strong>need</strong> to expose the
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<span class="tt">fetch-next</span> and <span class="tt">store-next</span> 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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<br/><br/>
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A recent change was the addition of the assembler into the
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kernel. This allows the higher levels to use assembly as needed,
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which gives more flexibility and allows for more optimal code
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in the standard library.
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<br/><br/>
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With these words the rest of the language can be built up. Note
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that the Retro 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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<br/><br/>
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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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<br/><br/>
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<tt class='indentedcode'>| Offset | Contains |</tt>
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<tt class='indentedcode'>| ------ | --------------------------- |</tt>
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<tt class='indentedcode'>| 0 | lit call nop nop |</tt>
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<tt class='indentedcode'>| 1 | Pointer to main entry point |</tt>
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<tt class='indentedcode'>| 2 | Dictionary |</tt>
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<tt class='indentedcode'>| 3 | Heap |</tt>
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<tt class='indentedcode'>| 4 | Retro version identifier |</tt>
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<br/><br/>
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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 <span class="tt">interpret</span> and <span class="tt">err:notfound</span>
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when implementing the user facing interface.
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</p>
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</body></html>
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