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.
incoming: 2026