EBF++ demo

demo.rkt

; Define variables a and b
:a :b

; Initialize a = 3, b = 2. $a is EBF for "go to the cell where a is stored."
$a 3+
$b 2+    ; (1) See footnotes below if you're not familiar with BF.

; Define a "pour" macro. Pour is BF's simplest version of "add". In another
; language, it might look like this: (of course, it's a macro, not a function)
;
;   void pour(*src, *dst) {
;       *dst = *src + *dst;
;       *src = 0;
;   }
{pour \ src \ dst \\  ; Macro arguments: src and dst. When the macro is
                      ; invoked, these will be variables like a and b.
  ; Macro body. % is the notation for argument substitution.
  %src [    ; (2)
    -
    %dst+
    %src
  ]
}

; Invoke the macro. It expands to:
;   $a [- $b+ $a]
&{pour / $a / $b}

; Now, a = 0 and b = 5. But how can we see that? We need some IO.
; Store a dot (ASCII 46) in a new variable...
:dot
$dot 46+

; ... and then print out b dots. You should see five dots appear as output.
$b [
  -
  $dot .    ; (3)
  $b
]

; Voila! Your first EBF++ program.



;;; Footnotes for BF newbies ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; (1) You found the first footnote! Yay.
;   + means "increment the current cell."
;   - means "decrement the current cell."

; (2) The pour pattern is common in BF.
;   [ ] means "loop while the current cell (i.e. the cell you're at when you
;     hit a bracket) is nonzero."
;   < means "move the pointer one cell to the left."
;   > means "move the pointer one cell to the right."
;
; So if you want to pour from one cell into a cell three to its right, you
; write:
;
;   [
;     -        ; Decrement the "source" cell.
;     >>> +    ; Increment the "destination" cell.
;     <<<      ; Move back to the original cell.
;   ]
;
; This macro is simply the "location-agnostic" version: It takes advantage of
; EBF++ variables to save the programmer from worrying about how many >'s and
; <'s to use.

; (3) . means "print a single character, reading the current cell as an ASCII
;       value."