Abhi-ctrl-cmd

type Row = [Int]
type Col = [Int]
type Board = [Row]

addDigit :: Row -> Int -> Int -> Board -> [Row] -- takes a row r, its index m, the index of a cell in it m, and the board; returns list of possble rows with that cell filled
addDigit r m n b = let pos = r !! n
                       c   = getCol n b
                       s   = concat (getSquare m n b)
                       fill    = intersection (left c) (left r) (left s) -- list of numbers that could be in cell (m,n)
                    in if (pos > 0) then [r]            -- cell already filled

Abhi-ctrl-cmd

In each iteration, the program checks if the current instruction is +/,/-/./</>/[/] (in that order). If it obtains a match, it executes the instruction, but does not restart the loop; eg if there is a "++" sequence, it executes the first one but compares the second one to a , then - etc, and cycles back to plus.

The tape is configured as follows:
1 = instruction counter (no of instructions executed in current iteration)*
2 & 3 = program counter PC
4 & 5 = tape counter TC
6 = bracket counter (for nested brackets) BC
7 = buffer (always 0 except for copying purposes)
8 = beginning of input program T1 (always 255 except for copying purposes)
9 etc = input program; each instruction takes 4 cells (x; x; 255; 255)