= || jump pen x |pen position| $oldx $y |@math| $x =
    |pen position| $x $y

= || jump pen y |pen position| $x $oldy |@math| $y =
    |pen position| $x $y

= || jump |backtrack| $row $col =
    |@math| multiply $col 2
    |@math| multiply $row 2
    || jump pen x || jump pen y
    |matrix position| $row $col
= || jump |generate| =

= || restore cells |discarded cells| $row $col = 
    |cells| $row $col || restore cells
= || restore cells =

= || delete cell |location| $row $col |cells| $row $col =
    || restore cells
= || delete cell |location| $row $col? |cells| $r $c =
    |discarded cells| $r $c
    || delete cell
= || delete cell |location| $row $col =
    || restore cells

= || prepare cells |cells| 127 |@math| 127 =
    |cells| 127 127

= || next column |@math| $col =
    |cells| 0 $col
    || prepare cells

= || prepare cells |cells| $col |@math| 127 =
    |@math|add $col 1
    |cells| 127 $col
    || next column

= || prepare cells |cells| $col |@math| $row =
    |@math| add $row 1
    |cells| $col
    |cells| $row $col
    || prepare cells

= || prepare cells |cells| $row $col =
    |@math| add $row 1
    |cells| $col
    |cells| $row $col
    || prepare cells

= || compute down $col |@math| $row =
    |down neighbor| $row $col

= || compute right $row |@math| $col =
    |right neighbor| $row $col

= || compute up $col |@math| $row =
    |up neighbor| $row $col

= || compute left $row |@math| $col =
    |left neighbor| $row $col

= || find valid neighbors? |down neighbor| $row $col |cells| $row $col =
    |discarded cells| $row $col
    |valid down neighbor| $row $col

= || find valid neighbors? |right neighbor| $row $col |cells| $row $col =
    |discarded cells| $row $col
    |valid right neighbor| $row $col

= || find valid neighbors? |up neighbor| $row $col |cells| $row $col =
    |discarded cells| $row $col
    |valid up neighbor| $row $col

= || find valid neighbors? |left neighbor| $row $col |cells| $row $col =
    |discarded cells| $row $col
    |valid left neighbor| $row $col

= || find valid neighbors? |cells| $row $col =
    |discarded cells| $row $col

= |up neighbor| $row $col =
= |right neighbor| $row $col =
= |down neighbor| $row $col =
= |left neighbor| $row $col =

= || find valid neighbors =
    || restore cells

= || find neighbors |location| $row $col =
    || compute down $col  |@math| add $row  1
    || compute right $row |@math| add $col  1
    || compute up $col    |@math| add $row -1
    || compute left $row  |@math| add $col -1
    || find valid neighbors

= || go in direction |@math| 1 |valid up neighbor| $row $col =
    || move up || move up
    || delete cell |location| $row $col
    |matrix position| $row $col || clear navigation state

= || go in direction |@math| 2 |valid right neighbor| $row $col =
    || move right || move right
    || delete cell |location| $row $col
    |matrix position| $row $col || clear navigation state

= || go in direction |@math| 3 |valid down neighbor| $row $col =
    || move down || move down
    || delete cell |location| $row $col
    |matrix position| $row $col || clear navigation state

= || go in direction |@math| 4 |valid left neighbor| $row $col =
    || move left || move left
    || delete cell |location| $row $col
    |matrix position| $row $col || clear navigation state

= || go in direction? |@math| 1 |sweep|=
    |@math| 2
= || go in direction? |@math| 2 |sweep|=
    |@math| 3
= || go in direction? |@math| 3 |sweep|=
    |@math| 4
= || go in direction? |@math| 4 |sweep|=
    |@math| 1

= || go in direction |@math| $n =
    || clear navigation state || jump

= || push location to backtrack stack |location| $row $col =
    |backtrack| $row $col

= || push location to backtrack stack =

= || clear navigation state? |valid up neighbor| $r $c =
    || push location to backtrack stack 
= || clear navigation state? |valid left neighbor| $r $c =
    || push location to backtrack stack 
= || clear navigation state? |valid down neighbor| $r $c =
    || push location to backtrack stack 
= || clear navigation state? |valid right neighbor| $r $c =
    || push location to backtrack stack 
= || clear navigation state? |sweep| =
= || clear navigation state =

= || pick a random direction |matrix position| $row $col =
    || find neighbors |location| $row $col
    || go in direction |location| $row $col |sweep| |sweep| |sweep|
    |@math| random 1 5

= || update |generate|? =
    || pick a random direction

==  
    |cells| 1 0 |matrix position| 0 0 |screen resolution| 256 256
    || prepare cells
    || pen brush pencil
    || pen down
    || pen color 255 255 255
    |generate|