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<p><span class="h2">On The Evolution Of Ngaro Into Nga</span>
<br/><br/>
When I decided to begin work on what became Retro 12, I knew
the process would involve updating Ngaro, the virtual machine
that Retro 10 and 11 ran on.
<br/><br/>
Ngaro rose out of an earlier experimental virtual machine I had
written back in 2005-2006. This earlier VM, called Maunga, was
very close to what Ngaro ended up being, though it had a very
different approach to I/O. (All I/O in Maunga was intended to be
memory mapped; Ngaro adopted a port based I/O system).
<br/><br/>
Ngaro itself evolved along with Retro, gaining features like
automated skipping of NOPs and a LOOP opcode to help improve
performance. But the I/O model proved to be a problem. When I
created Ngaro, I had the idea that I would always be able to
assume a console/terminal style environment. The assumption was
that all code would be entered via the keyboard (or maybe a
block editor), and that proved to be the fundamental flaw as
time went on.
<br/><br/>
As Retro grew it was evident that the model had some serious
problems. Need to load code from a file? The VM and language had
functionality to pretend it was being typed in. Want to run on
something like a browser, Android, or iOS? The VM would need to
be implemented in a way that simulates input being typed into
the VM via a simulated keyboard. And Retro was built around this.
I couldn't change it because of a promise to maintain, as much
as possible, source compatibility for a period of at least five
years.
<br/><br/>
When the time came to fix this, I decided at the start to keep
the I/O model separate from the core VM. I also decided that the
core Retro language would provide some means of interpreting
code without requiring an assumption that a traditional terminal
was being used.
<br/><br/>
So Nga began. I took the opportunity to simplify the instruction
set to just 26 essential instructions, add support for packing
multiple instructions per memory location (allowing a long due
reduction in memory footprint), and to generally just make a far
simpler design.
<br/><br/>
I've been pleased with Nga. On its own it really isn't useful
though. So with Retro I embed it into a larger framework that
adds some basic I/O functionality. The <strong>interfaces</strong> handle the
details of passing tokens into the language and capturing any
output. They are free to do this in whatever model makes most
sense on a given platform.
<br/><br/>
So far I've implemented:
<br/><br/>
<tt class='indentedcode'>-&nbsp;a&nbsp;scripting&nbsp;interface,&nbsp;reading&nbsp;input&nbsp;from&nbsp;a&nbsp;file&nbsp;and</tt>
<tt class='indentedcode'>&nbsp;&nbsp;offering&nbsp;file&nbsp;i/o,&nbsp;gopher,&nbsp;and&nbsp;reading&nbsp;from&nbsp;stdin,&nbsp;and</tt>
<tt class='indentedcode'>&nbsp;&nbsp;sending&nbsp;output&nbsp;to&nbsp;stdout.</tt>
<tt class='indentedcode'>-&nbsp;an&nbsp;interactive&nbsp;interface,&nbsp;built&nbsp;around&nbsp;ncurses,&nbsp;reading</tt>
<tt class='indentedcode'>&nbsp;&nbsp;input&nbsp;from&nbsp;stdin,&nbsp;and&nbsp;displaying&nbsp;output&nbsp;to&nbsp;a&nbsp;scrolling</tt>
<tt class='indentedcode'>&nbsp;&nbsp;buffer.</tt>
<tt class='indentedcode'>-&nbsp;an&nbsp;iOS&nbsp;interface,&nbsp;built&nbsp;around&nbsp;a&nbsp;text&nbsp;editor,&nbsp;directing</tt>
<tt class='indentedcode'>&nbsp;&nbsp;output&nbsp;to&nbsp;a&nbsp;separate&nbsp;interface&nbsp;pane.</tt>
<tt class='indentedcode'>-&nbsp;an&nbsp;interactive&nbsp;block&nbsp;editor,&nbsp;using&nbsp;a&nbsp;gopher-based&nbsp;block</tt>
<tt class='indentedcode'>&nbsp;&nbsp;data&nbsp;store.&nbsp;Output&nbsp;is&nbsp;displayed&nbsp;to&nbsp;stdout,&nbsp;and&nbsp;input&nbsp;is</tt>
<tt class='indentedcode'>&nbsp;&nbsp;done&nbsp;via&nbsp;the&nbsp;blocks&nbsp;being&nbsp;evaluated&nbsp;or&nbsp;by&nbsp;reading&nbsp;from</tt>
<tt class='indentedcode'>&nbsp;&nbsp;stdin.</tt>
<br/><br/>
In all cases, the only common I/O word that has to map to an
exposed instruction is <span class="tt">putc</span>, to display a single character to
some output device. There is no requirement for a traditional
keyboard input model.
<br/><br/>
By doing this I was able to solve the biggest portability issue
with the Retro 10/11 model, and make a much simpler, cleaner
language in the end.
</p>
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