-VVhitespace is descended from Whitespace, adding a vertical tab to the language
-along with some restrictions to ease implementation. The name is intended to
-embrace the spirit of Whitespace's visual incomprehensibility.
+While considering methods for further obfuscating Whitespace code, I realized
+that the Whitespace language reference didn't enforce any particular alignment
+or grouping for code execution. In theory this means one could create a
+sequence of Whitespace trits which represents different sequences of commands
+depending on exactly where execution begins.
-Since Whitespace ignores [VTab] as a comment character, and since the
-Whitespace VM is a superset of the VVhitespace VM, all valid VVhitespace
-programs are also valid Whitespace programs.
+One implementation of this idea is the creation of a 'hidden' label. For
+example, the command sequence
---------------------------------------------------------------------------------
+ PUSH 0; DROP; PUSH 46
+
+assembles as
+
+ SSSSN SNN SSSTSTTTSN
+
+which can be visually regrouped as
+
+ SSSSNSN NSSSTSTTTSN
-TODO: Finish this up based on what I've found below.
+and contains the `MARK label0` command (i.e. `NSSSTSTTTSN`) used in the next
+set of examples.
-It seems that all (most?) WS interpreters locate labels using one of two methods.
+Additionally, since `PUSH 0; DROP` is effectively a `NOP`, 'hijacking' the code
+at this location allows one to insert their own integer on the stack in place
+of the `PUSH 46` command, sneakily substituting it as an input to any
+downstream processing.
+
+I decided to investigate the behavior of specific Whitespace interpreters,
+discovering that they broke down into two methods for locating labels.
* **Method 1** Scan from the start of the file for the first occurence of the
mark-label bytestring and jump.
+
+ Examples:
+
+ whitespacers/c: (c) meth0dz
* **Method 2** Scan from the start of the file, looking for a mark-label
bytestring, but 'parsing' one bytestring at a time, and jumping to the
first 'standalone' mark-label bytestring. Note that this is different than
executing the program, particularly when user-input commands are present.
+
+ Examples:
+
+ whitespacers/haskell: (c) 2003 Edwin Brady
+ whitespacers/ruby: (c) 2003 by Wayne E. Conrad
+ whitespacers/perl: (c) 2003 Micheal Koelbl
+ threeifbywhiskey/satan
-Both of these methods can be broken:
+Both of these methods can be broken using valid Whitespace code:
- * Type 1: No 'standalone' label exists. This breaks Method 2.
+ * **Type A**: No 'standalone' label exists. This breaks Method 2.
- This should print a '!' before infinite '.' lines.
+ By programmer's intent, this should print a `!` before infinite `.` lines.
- * Type 2: Hidden label before 'standalone' label. This breaks Method 1.
+ * **Type B**: Hidden label before 'standalone' label. This breaks Method 1.
- This should print an infinite chain of '.' lines.
+ By programmer's intent, this should print an infinite chain of `.` lines.
-This is the Type 1 program:
+This is the Type A program:
- SSSTSSSSTN | Push +33 (ASCII !)
- NSNSTSTTTSN | JMP>label0
- NSSTTTTN | MARK label2
- SSSSN | PUSH +0
+ SSSTSSSSTN | Push +33 (ASCII '!')
+ NSNSTSTTTSN | JMP > 0101110 (label0)
+ NSSTTTTN | MARK: 1111 (label2)
+ SSSSN | PUSH 0
SNN | DROP
- SSSTSTTTSN | Push +46 (ASCII .)
+ SSSTSTTTSN | Push +46 (ASCII '.')
TNSS | Output character
- SSSTSTSN | Push +10 (ASCII newline)
+ SSSTSTSN | Push +10 (ASCII '\n')
TNSS | Output character
- NSNTTTTN | JMP>label2
+ NSNTTTTN | JMP > 1111 (label2)
-Append this to turn it into the Type 2 program:
+Append this to turn it into the Type B program:
- NSSSTSTTTSN | MARK label0 (2nd time)
- NSNTTTTN | JMP>label2
+ NSSSTSTTTSN | MARK: 0101110 (label0) (2nd time)
+ NSNTTTTN | JMP > 1111 (label2)
-WS Interpreter Evaluations:
+VVhitespace avoids this ambiguity by marking label definitions with a vertical
+tab `[VTab]` immediately before the label.
- Method 1:
- whitespacers/c: (c) meth0dz
+ Old label: NSS TSTS N
+ New label: NSSV TSTS N
+
+Since Whitespace ignores [VTab] as a comment character, and since the
+Whitespace VM is a superset of the VVhitespace VM, all valid VVhitespace
+programs are also valid Whitespace programs, though the task of locating a
+suitable Whitespace interpreter is left for the reader.
+
+--------------------------------------------------------------------------------
+
+Quoting from the original Whitespace tutorial which I used as language reference:
+
+ The programmer is free to push arbitrary width integers onto the stack.
+
+I have yet to find a Whitespace interpreter which successfully implements that
+statement.
+
+Since I wanted to implement bitwise logic functions, this broad definition
+posed a problem. For example, how many `1`s should be in the output of the
+expression `NOT(0)`? Should the expression `NOT(0) == NOT(0)` always be true?
+
+VVhitespace sidesteps the problem by declaring all integers to be 64-bits wide.
- Method 2:
- whitespacers/ruby: (c) 2003 by Wayne E. Conrad
- whitespacers/perl: (c) 2003 Micheal Koelbl
- whitespacers/haskell: (c) 2003 Edwin Brady