Specfication for BFLX

bflx.spec

language specification for level extended brainfuck 
rev alpha.0

-- what

Yet another riff on the brainfuck language.

-- program structure
A bflx program is a sequence of byte codes (with ASCII semantics) of minimum length of 1.
    
-- memory model
  
- bflx maintains a list of data cell arrays.
- a data cell has unsigned 8-bit integer semantics.
- all bflx programs have at least one data array (index 0).
- data cell array index underflow semantics are the same as a circular buffer. 
- Index overflow will dynamically extend the given cell array.
- data cell arrays (levels) are navigated via cursor commands.
- bflx runtime maintains a single register.
  
-- data cursor commands
  
^ : level up    
  - move up to previous data array index.
  - if already at level 0, then go to the last.
 
v : level down
  - move down to the next data array index.
  - if already at level max, allocate a new layer and move to that.
  - data array levels are stateful and maintain their own data index.
      
< : move back
 - decrement data index of current data array. 
 - if data index is 0, then move index to the last position (per circular buffer semantics).
     
> : move forward
 - increment the data index of current data array.
 - if index overflows the array, grow it.

| : initial position
   - set data index of current level to 0.
   
. : final position
   - set data index of current level to last position.
     
-- Data access commands

+ : increment data cell by 1.
- : decrement data cell by 1.
~ : invert bits of current data cell

-- Register commands

# : copy current data cell to register
% : write register to current data cell

-- embedded data 

$ : treat all bytes until matching '$' as embedded data. data index incremented by length of embedded data.
   
-- IO commands
   
? : read a byte from stdin unto current data cell. data index incremended by 1.
! : write current data cell byte to stdout. data index incremented by 1.
n : write the numeric value of current byte (per printf("%d", b) i.e. byte value 27 -> "27")
N : write the zero-padded numeric value of current byte (per printf("%03d", b) i.e. byte value 27 -> "027")    
     
# control flow
[ : if current cell value is 0, move to next command after the matching ']'.
] : if current cell value is not 0, move to the next command after the matching '['.

-- example: hello world!
  
$hello world!$|!!!!!!!!!!!!