Befalse Interpreter in JavaScript

Befalse Interpreter

Befalse combines the stack flexibility of False with the 2-D code space and control flow of SNUSP. Unlike Befunge, the code space does not wrap, and the direction and branch operators (<>^v|_#) are replaced with the reflection and skip-if-zero operators of SNUSP (/\?!). Take a look at the JavaScript source.

Commands:

Basic stack operators: $DUP #DROP ^OVER %SWAP (^^2DUP %^TUCK)
Return stack: :CALL ;RET {PUSH }POP ({%}%ROT %{%}-ROT {$}%OVER {^}%THIRD)
Direction: /RULD \LURD from SNUSP
Choice: ?SKIPZ !SKIP (?!SKIPNZ) from SNUSP
Math: +ADD -SUB *MUL `DIVMOD ( n d -- n%d n/d ) _NEGATE
Logic: &AND |XOR ~NOT (^~&|OR)
Comparison: <LT >GT (0 false, -1 true; use ab-?! for EQ)
I/O: .EMIT ,KEY (characters) 'INPUT (number)
Memory: @FETCH =STORE (these are named 'g' and 'p' in Befunge)
Digits: 0-9 push their value, like Befunge
Number mode: (1234) make larger numbers with parentheses
String mode: " starts and ends string mode, like Befunge

Missing from Befunge: random command, stack underflow, toroidal code space

Samples:

world!

0"!dlrow olleH"!/$?\
                \. /
0"Hello world!"!/$?\#;
             ;.}\:{/

a number

(1234!/55+`$?\\
      \   /!://
    ;.+*68/!#/

(greatest common divisor)

''$!/#$?\#
    \`^%/

number

'{01!/% }$?\##
     \+^{-1/

of Eratosthenes

2!/$4@" "-?!\$!/^+$(80<  ?\\
  \?<9$   +1/!#\=4=3^^^" "//
               \          /
          1111111111222222222223333333333444444444455555555556666666666777777777
  234567890123456789012345678901234567890123456789012345678901234567890123456789

on a chess board without attacking each other. Change 255 to 2ⁿ-1 for an nxn board.

015=0~$(255:\15@;
            \!/$?\15@1+15= $!/####;
                 \{^^&}%^&$?!/${$_&~$${{{{^}%}&2*1+{\
              \              ?!      \              ^
                             \$ &-1$}\:&}%}^{+`2&}%}/
[0]

of beer

Befalse IAO    (99!/:\" ,"..:\55+"."..\
/ :`+55\          ;\? $.."."+ 55/:-1\ !
!  /   \?>9$$\       :          :      
/  /"no more"\?$/!: !/! ! ! !/! /     !
8  \ .......;                       !  
6     /" bottle"/    !          !     !
*     \ .......$1-?!\"s"\           !  
+        /" of beer"/! ./       !     !
.        \ ........;                !  
;     /" on the wall"/! ! ! ! ! /     !
      \ ............;               !  
 /"Take one down and pass it around, "/
 \................................../

!/,0^>?;$(32^~&|"a"^>?\$"z">?\(13%"m"\
 \. ! ! ! ! ! ! ! ! !#/! ! ! /!$ +_?>/

function

''\ / recursion \! \!\
ji\!\$?\#1+;
       \^?\1-%1+ %:/;
          \%1-^:/%1-:/;

or times ms

Input
Stack
Output:

Caveats

Code may not line up correctly if modifed with the store (=) instruction.
The code space is only as large as the initial program. Insert more lines or trailing space if data will be put beyond the end of code.
Width is one more than you would expect, due to terminal newlines.
When using the Run button, you cannot interrupt an infinite loop.
Tested in Safari 1.3 and IE 6

0"om.cerstrkui@qnoia"!/ $?\
                      \..%/