Translate RoboCritters into Brainf***

Question

RoboCritters (etymology) is a brand new esoteric programming language (don't bother searching for it, I just invented it). It's a variant of Brainfuck (BF), slightly more complex than the usual operator substitution schemes. Every program in RoboCritters is a rectangular grid of text that only contains the seven characters . []/\|, plus newlines to shape the grid.

Example RoboCritters program:

|\/||./|[]||
[..][][]   |
|/\|[..][..]
[..]    \/\/

To translate a RoboCritters program into BF, look at each non-newline character in the grid in the normal reading order (left-to-right then top-to-bottom), e.g. |\/||./|[]||[..][][] ||/\|[..][..][..] \/\/.

If the 4×2 section of the grid extending right and down from the current character exactly matches one of the eight robot critters listed below, append the corresponding BF command (><+-.,[]) to the (initially empty) BF program.

If the 4×2 grid section does not match any of the robot critters or goes out of bounds, nothing is added to the BF program.

1. Joybot, > command:

   [..]
   \][/
   

2. Calmbot, < command:

   [..]
   /][\
   

3. Squidbot, + command:

   [..]
   //\\
   

4. Spiderbot, - command:

   [..]
   ||||
   

5. Bunnybot, . command:

   [][]
   [..]
   

6. Toothbot, , command:

   [..]
   |/\|
   

7. Foxbot, [ command:

   |\/|
   [..]
   

8. Batbot, ] command:

   [..]
   \/\/
   

So, reading the example program

|\/||./|[]||
[..][][]   |
|/\|[..][..]
[..]    \/\/

we can see that we first encounter a Foxbot (at column 1, row 1), then a Toothbot (c1,r2), then a Bunnybot (c5,r2), and finally a Batbot (c9,r3). This corresponds to the BF program [,.].

Notice that the Foxbot and Toothbot overlap. This is intentional; robot critters are not interpreted any differently when they overlap.

Challenge

Write the shortest program possible that takes in a RoboCritters program and outputs its BF equivalent. You don't need to run the BF or check that it's valid, only translate the RoboCritters code to BF code.

Details

• All input RoboCritters programs will be valid, that is they will be an exactly rectangular block of text only containing the seven characters . []/\|, plus newlines to shape it. The newlines may be in any convenient common representation. You may optionally assume the programs have a single trailing newline.

• You must support RoboCritters programs that are smaller than 4×2, including the 0×0 empty (or single newline) program. These all correspond to the empty BF program (the empty string).

• The output BF program should be a one-line string only containing the eight BF command characters ><+-.,[]. There may optionally be a single trailing newline.

• Take input in any usual way (stdin/text file/command line) and output to stdout or your language's closest alternative.

• Instead of a program you may write a function that takes the RoboCritters program as a string and prints or returns the BF program string.

Examples

1. Input: (variant of example above)

   |\/|[][]
   [..][][]
   |/\|[..]
       \/\/
   

   Output: [,.]

2. Input: (tests all robot critters)

   [..][[[[[..]]. ]|\/|
   \][/[..]//\\[..][..]
   [..]/][\[][]|/\|[..]
   ||||/\| [..]|  |\/\/
   

   Output: >+[<,-.]

3. Input:

   [..] [..] [..] [..] [..] [..] [..] [..] |\/| [..] [..] [..] [..] [..] |\/| [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] [..] |\/| [..] [..] [..] [..] [..] [..] [..] [][] [..] [..] [..] [..] [][] [..] [..] [..] [..] [..] [..] [..] [][] [][] [..] [..] [..] [][] [..] [..] [][] [..] [..] [][] [..] [][] [..] [..] [..] [][] [..] [..] [..] [..] [..] [..] [][] [..] [..] [..] [..] [..] [..] [..] [..] [][] [..] [..] [..] [][] [..] [..] [..] [][]
   //\\ //\\ //\\ //\\ //\\ //\\ //\\ //\\ [..] \][/ //\\ //\\ //\\ //\\ [..] \][/ //\\ //\\ \][/ //\\ //\\ //\\ \][/ //\\ //\\ //\\ \][/ //\\ /][\ /][\ /][\ /][\ |||| \/\/ \][/ //\\ \][/ //\\ \][/ |||| \][/ \][/ //\\ [..] /][\ \/\/ /][\ |||| \/\/ \][/ \][/ [..] \][/ |||| |||| |||| [..] //\\ //\\ //\\ //\\ //\\ //\\ //\\ [..] [..] //\\ //\\ //\\ [..] \][/ \][/ [..] /][\ |||| [..] /][\ [..] //\\ //\\ //\\ [..] |||| |||| |||| |||| |||| |||| [..] |||| |||| |||| |||| |||| |||| |||| |||| [..] \][/ \][/ //\\ [..] \][/ //\\ //\\ [..]
   

   Output: (BF Hello World program)

   ++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.
   

4. Input: (no robot critters present)

   /\\\[].
   ]..[..]
   \\//||\
   

   Output: (empty string)

Scoring

The shortest submission in bytes wins. (Handy byte counter.) Tiebreaker is highest voted post.

Answer 1

CJam, 86 85 bytes

qN/S4*f+_W<\1>]z:z4few:~"¨Ý³5&ágûò{wÉ](Ý"296b6b"|[\.]/"f=2/4/"><+-.,[]":Ler{L&},

Test it here.

Explanation

qN/    e# Read input and split into lines.
S4*f+  e# Append four spaces to each line. This has two purposes. a) We can later join all
       e# the lines together without worrying about critters appearing across the line
       e# edges because no critter contains spaces. b) It works around a bug in CJam where
       e# the command `ew` crashes when the substring length is longer than the string.
_W<    e# Copy the lines and discard the last one.
\1>    e# Swap with the other copy and discard the first one.
]z     e# Wrap both in an array and zip them up. Now we've got an array which contains
       e# all consecutive pairs of lines.
:z     e# Zip up each of those pairs, such it becomes an array of two-character strings.
       e# We can now find the critters as 4-element subarrays in each of those arrays.
4few   e# Turn each of those arrays into a list of its (overlapping) 4-element subarrays.
:~     e# Flatten those lists, such that we get one huge array of all 4x2 blocks, in order.
"gibberish"296b6b
       e# This is an encoded form of the critters. The above produces a string of the
       e# critters in column-major order, all joined together, where the characters are
       e# represented by numbers 0 to 5.
"|[\.]/"f=
       e# Turn each number into the correct character.
2/4/   e# Split first into columns, then into critters. Now all we need to do is find these
       e# the elements of this array in the processed input.
"><+-.,[]":L
       e# A string of all BF characters in the same order as the critters. Store this in L.
er     e# Do an element-wise replacement. This will leave non-critter blocks untouched.
{L&},  e# Filter the result. The elements are now either characters, or still full 4x2
       e# blocks. We take the set intersection with the array (string) of BF characters.
       e# If the current element is itself a character, it will be coerced into an array
       e# containing that character, such that we get a non-empty intersection. If the
       e# current element is a block instead, if contains arrays itself, so the set
       e# intersection will always be empty.

       e# The resulting array of characters is the desired BF program and will be printed
       e# automatically at the end of the program.

The critters were encoded with this script. I found the base 296 for the encoding with the following, rather naive Mathematica script (which is still running in search for a better base):

b = 256;
While[True,
  If[
    FreeQ[
      d = IntegerDigits[15177740418102340299431215985689972594497307279709, b], 
      x_ /; x > 255
    ], 
    Print@{b, Length@d}
  ];
  b += 1;
]

Answer 2

JavaScript ES6, 209 198 192 bytes

f=c=>{s=''
b=o=>c.substr(o,4)||1
for(i in c)s+=!~(d='1\\][/1/][\\1//\\\\1||||[][]11|/\\||\\/|11\\/\\/'.replace(/1/g,'[..]').indexOf(b(i)+b(++i+c.search(`
`))))|d%8?'':'><+-.,[]'[d/8]
return s}

The Stack Snippet below contains ungolfed code that you can easily run in any browser.

var f = function(c) {
  var s = '';
  var b = function(o) {
    // If it is looking on the last line, this will return an empty string
    // the second time, which could cause an inaccurate match.
    // `||1` makes it return 1 instead of '', which won't match.
    return c.substr(o, 4) || 1;
  }
  for (var i in c) {
    r = b(i) + b(++i + c.search('\n'));
    d = '1\\][/1/][\\1//\\\\1||||[][]11|/\\||\\/|11\\/\\/'.replace(/1/g, '[..]').indexOf(r);
    s += !~d || d % 8 ? '' : '><+-.,[]' [d / 8];
  }
  return s;
}

// GUI code below
function run(){document.getElementById('s').innerHTML=f(document.getElementById('t').value);};document.getElementById('run').onclick=run;run()

<textarea id="t" cols="30" rows="10">
[..][[[[[..]]. ]|\/|
\][/[..]//\\[..][..]
[..]/][\[][]|/\|[..]
||||/\| [..]|  |\/\/</textarea><br /><button id="run">Run</button><br /><code id="s"></code>