M/PC – A Concatenative OS

M/PC is a concatenative operating system for Varvara, inspired by Openfirmware, designed to manage files on system without a file browser. It uses the postfix notation, meaning that the function success their operands:

( Get the number of bytes in folder/file_name )
folder/ file_name cat len dec

Files can store reusable sequences of commands, the tilde prefix includes the content of the file:

( Content of ./show-slide )
slide_ swp cat 3cx22.icn cat 1 icn

1 ~show-slide

The interface uses a single prompt at the top of the screen to input commands:

Controls

The operating system can be used largely without a keyboard to navigate folders and launch roms:

• left/right Navigate Stack
• up/down Scroll Stack
• A Evaluate Selected Symbol
• B Directory/Back

Kiosk

To start M/PC as a BIOS rom so that when the user presses F4, Varvara returns to the BIOS instead of triggering a reboot, launch with arguments:

uxnemu m_pc.rom orca.rom run

Wallpaper

On boot, M/PC will try and draw an ICN file named wallpaperWWxHH.icn, where WW is the width of the screen divided by 8 in hexadecimal, and HH the height.

Reference

Here is the list of all primitives:

dir ( -- [f] )
	Put the file names in the current location on the stack.
mov ( path -- [f] )
	Move the current location to current/path, then do dir.
now ( -- date time )
	Puts the date Tue, 23 Jun 2026, and time 11:48:45 on the stack.
run ( f.rom -- ok )
	Run the rom file, return with F4.
icn ( f.icn blend -- ok )
	Draw an icn file with blend.
txt ( f.txt line -- ok )
	Read a text file starting at line.
len ( f -- hex )
	Put the length of a file in hexadecimal.
put ( body f -- ok )
	Create a file with the content of body.
get ( f -- body )
	Put the content of a file on the stack.
cpy ( fsrc fdst -- ok )
	Copy the content of fsrc into fdst.
era ( f -- ok )
	Erase file.
ren ( fsrc fdst -- ok )
	Rename file fsrc into fdst.
pop ( a -- )
	Pop symbol at the top of the stack.
dup ( a -- a a )
	Duplication symbol at the top of the stack.
ovr ( a b -- a b a )
	Copy second symbol to the top of the stack.
swp ( a b -- b a )
	Pull the second symbol to top.
rot ( a b c -- b c a )
	Pull the third symbol to top.
add ( a b -- a+b )
	Push the sum of two symbols.
sub ( a b -- a-b )
	Push the difference of two symbols.
dec ( hex -- dec )
	Convert hexadecimal number to decimal.
hex ( dec -- hex )
	Convert decimal number to hexadecimal.
cat ( a b -- ab )
	Concatenate two symbols.
cmp ( a b -- bool )
	Compare the names of two symbols.
and ( a b -- bool )
	Put true if both symbols are true.
ora ( a b -- bool )
	Put true if either symbol is true.
rsz ( width height -- )
	Resize the screen, puts true if resize is supported by Screen.
out ( a -- )
	Output symbol to Console/write.
bye ( -- )
	Quit.

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