[Question]
  [
Your challenge is simple: write as long of a [pristine program](https://codegolf.stackexchange.com/questions/63433/programming-a-pristine-world) as possible in the language of your choice using only unique bytes. (The full definition of a pristine program, copied from that link, is at the bottom of this question.)
That's right, no strings attached. Your code doesn't have to do anything at all, just run without erroring, meet the requirements for a pristine program (linked above), and include no duplicate bytes in the encoding you use.
For the purposes of the above explanation and linked definition of "pristine program", an error is defined as anything that causes the program to either entirely fail to run or to terminate with a nonzero exit code after a finite amount of time.
As this is [code-bowling](/questions/tagged/code-bowling "show questions tagged 'code-bowling'"), ***longest***, not shortest, code wins (measured by byte count). The maximum theoretically possible score is 256, as there are 256 distinct bytes possible. In case of a tie, the first answer at the highest score wins.
---
Here's the full definition of a pristine program, copied from the above link:
> 
> Let's define a *pristine program* as a program that does not have any errors itself but will error if you modify it by removing any contiguous substring of N characters, where `1 <= N < program length`.
> 
> 
> For example, the three character Python 2 program
> 
> 
> 
> ```
> `8`
> 
> ```
> 
> is a pristine program because all the programs resulting from removing substrings of length 1 cause errors (syntax errors in fact, but any type of error will do):
> 
> 
> 
> ```
> 8`
> ``
> `8
> 
> ```
> 
> and also all the programs resulting from removing substrings of length 2 cause errors:
> 
> 
> 
> ```
> `
> `
> 
> ```
> 
> If, for example,  ``8` had been a non-erroring program then ``8`` would not be pristine because **all** the results of substring removal must error.
> 
> 
> 
  
[Answer]
# [Haskell](https://www.haskell.org/), ~~39~~ ~~45~~ ~~50~~ ~~52~~ 60 bytes
```
main=do{(\§∂∏	Ôßì¬†‚µô
ÂïÜ
ﬂú·öÄÊñ∞->pure fst)LT
EQ[]3
2$1}
```
Identifier `main` has to have type `IO a` for some type a. When the program is executed, the computation `main` is performed, and its result is discarded. In this case its type is `IO ((a,b)->a)`. 
The result is an application of the function `(Œª a b c d e f ‚Üí return fst)`,
a six-argument constant function returning the function fst (which gives the first element of a 2-tuple), injected into the IO monad. The six arguments are `LT` (enum for less than), `EQ` (enum for equality), empty list `[]`, `3`, `2` and `1`.
What would be spaces are replaced with unique characters that count as spaces: a tab, a non-breaking space, a formfeed, vertical tab, OGHAM SPACE MARK, regular space, newline and carriage return. If any of these are missing, there will be a mismatch in the number of arguments. The parameter names are chosen as three or four byte UTF-8 characters, `§∂∏Ôßì‚µôÂïÜﬂúÊñ∞`, carefully choosing characters that don't result in duplicate bytes. 
Thanks to @BMO for his valuable contributions.
Hex dump:
```
00000000: 6d61 696e 3d64 6f7b 285c f0a4 b6b8 09ef  main=do{(\......
00000010: a793 c2a0 e2b5 990c e595 860b df9c e19a  ................
00000020: 80e6 96b0 2d3e 7075 7265 2066 7374 294c  ....->pure fst)L
00000030: 540a 4551 5b5d 330d 3224 317d            T.EQ[]3.2$1}
```
[Try it online!](https://tio.run/##AUcAuP9oYXNrZWxs//9tYWluPWRveyhc8KS2uAnvp5PCoOK1mQzllYYL35zhmoDmlrAtPnB1cmUgZnN0KUxUCkVRW10zCjIkMX3//w "Haskell ‚Äì Try It Online")
[Answer]
# [Jelly](https://github.com/DennisMitchell/jelly), ~~253 254~~ 256 bytes
```
M‚Äú¬¢¬£¬•¬¶¬©¬¨¬Æ¬µ¬Ω¬ø‚Ç¨√Ü√á√ê√ë√ó√ò≈í√û√ü√¶√ß√∞ƒ±»∑√±√∑√∏≈ì√æ !"#%&'()*+,-./0145689:;<=>?@ABCDEFGHIJKNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|~¬∂¬∞¬π¬≤¬≥‚Å¥‚Åµ‚Å∂‚Å∑‚Å∏‚Åπ‚Å∫‚Åª‚Åº‚ÅΩ‚Åæ∆Å∆á∆ë∆ì∆ò‚±Æ∆ù∆§∆¨∆≤»§…ì∆à…ó∆í…†…¶∆ô…±…≤∆• †…º Ç∆≠ ã»•·∫†·∏Ñ·∏å·∫∏·∏§·ªä·∏≤·∏∂·πÇ·πÜ·ªå·πö·π¢·π¨·ª§·πæ·∫à·ª¥·∫í»¶·∏Çƒä·∏äƒñ·∏ûƒ†·∏¢ƒ∞ƒø·πÄ·πÑ»Æ·πñ·πò·π†·π™·∫Ü·∫ä·∫é≈ª·∏Ö·∏ç·∫π·∏•·ªã·∏≥·∏∑·πÉ·πá·ªç·πõ·π£·π≠·ª•·πø·∫â·ªµ·∫ì»ß·∏Éƒã·∏ãƒó·∏üƒ°·∏£≈Ä·πÅ·πÖ»Ø·πó·πô·π°·π´·∫á·∫ã·∫è≈º‚ÄùL¬ª¬´‚Äô∆ä·∫°‚Äò}237$¬§¬°
```
[Try it online!](https://tio.run/##Dc3nUlpBHIfhW0nvvffee@89McWYXk0bFgsGNIkwI5BEpTuJSAAF9r8HcWb3sHMOd/HbGyF8f@Z929s6OjqbzePG81smZFKmZUb@kVmZkyU5LWeMN6t6lU/9UIMqrCL1oBpRoyqjxlTeLjgVVVAVxeshVZs1e87c@QsWLlq8ZOmy5StWrlq9bv2GTZu3bN22fcfOXbv37N23/8DBQ4ePHD1x8tTpM2fPnb9w8dLlK1evXb9x89btO3fvtd1/8PBR@@OOJ0@fPX/x8tXrN2/fve/88PHTF1mWeUmyKCcNmzKsZFjZsIph3DAyTBhmGVY1bNqwmmbapwd1SEdMIaeHdUpnddFJuSHd54Z10I25GR11C25Rpxsxt9rw6olGwElDxMC7wfshOHgKlh@8CF4GeUG9sPpBP0EJUBZWClSD6IM1BRF0MuBeu6X99hD4iN3KJOy8PQPygLqdHGgIFAHFQH8heiH8EN/qFngP@AAEgadhBcAnwSugLpAP1gDoFygJmoCVBs1AfIVVggg5Y@BddksH7DD4qB0HT9ZbHwbqcf6BwqAoKA4ah/BBBCC@16vGM3xMWnLceKK6NY8bT@TzmrUb58mUjDeb/wE "Jelly ‚Äì Try It Online") or [Verify it!](https://tio.run/##rVLtV9tUGP9s/orraxqLWJyvaJk4ik7nUDdfgWFpb7fMNOmSFKlvp2EbTNjUwTkD1G28tOzoGAM2IDdhcM5NmtPyXzz5RzBJsaHqR@@H5N4nv5cnv/vkCuo5STyyn5LSOM6y7Ptu8Xe6QBdpmS7RP@gyXaEb9BHddUeWrVFrzPrFum5NWzOVSeuWddtasu5Yq/Zadctas7YsvTJl7aDHn3jy6WfYCPdstOW51udjbS@@9PKrr7W//ka84@ibnW8d60p0v/3O8XffO9nzwYcfnTr98Seffvb5F719/WcGvkwOptI4c/Ycf/4rIStKuQuyouaHvh4ufPPtdz/QTbpKCV2nD1ztoattuNqmq225mu5qxNUMVzNdbdvVHrnajqM5Y851Z8qZcddWnJtOyVl21qul2pRzpTbtTNbmakvObG2ttu6U9@Zq23sjzr29iWoZjDnQL4F@FQwd9BKY46Cvg74JZATIKJhXgfwKZAHIMpglIDtgXAHzIRiT1SXQR2wPPW7fAP2W7cks2Kv2LpAikEvVFSA3gMwAmQPyJxijYIyD8VPFBP0y6NfAIKCXwZwA/QHoW0AuAhkD8xqQ34AsArkHZhnILhg/grkBxlT1DugXbQ89YU@DftueB32x4vloQC5X7wOZBjILZB7IXTDGwJgA4@fKtlu8eYKa9K5bnHU883m3OPP9C0deeYqW6Lx36fsZWcqi81gQCojP5iRZrR8G8FBSYA4qKp/FDKPG4v6m1X9EOIbhM0jAYsQfHy4e97cKVutHrp15LCfzohpRVDnSQHEoiliUF/kLeYwGCypWWlmOwYKCG3g2McwrKkrncwKfSqqHYIwoiQlZlmQFxVGMSUl5UfV2bQyTkWSkqEmvUV5EclI8i0PLaJvXC/KWD8JiOoQEjGhbSwitlzpi3AHFX3WbqO8TltJ4QJX5bBanvQb8Y297QO33/i84ekbt/Q2CKhdCQX/JWMkLfvNh1JHDqi29/VyDgIdTOKc2C@SSihICgvwOfw6Tamo8YAYpN5n5scTZPrFPPNbTlUBdPYlT6GTPadTdefyEX2W5/1GBYQ7u2au2BDS2PkqNnjti9Z85wHUOSkMY/R23b4vSElY8vIqwTwhH6DBLEJo5AbQ@R43r@Ef6Qer1tFEiePGS2KTanfdkA7lMkheU/3QOMf9qc3//Lw)
Turns out golfing languages can bowl...
* +1 byte by working in `‚Äò`. ~~Now only `¬´¬ª` are not used~~
* +2 bytes with with `¬´¬ª`. Now have the optimal score!
## How?
The crucial feature of Jelly that makes this possible is that the opening and closing characters for string literals are not the same like in nearly all other languages.
The program structure is as follows:
`M <239 character long string> L¬ª¬´‚Äô∆ä·∫°‚Äò}237$¬§¬°`
`M` finds the indices of its argument that point to maximal elements. All that matters is that with no argument to this program Jelly assigns `0` to the chain and Jelly errors when `M` is applied to `0`. 
To prevent `M` from acting on `0` in the full program, we use the `¬°` quick, which applies `M` a number of times determined by the result of the link immediately preceding it. In this case that link is `<239 character long string> L¬ª¬´‚Äô∆ä·∫°‚Äò}237$¬§`.
`L` takes the length of this string (239), and `¬ª¬´‚Äô∆ä` decrements this to 238. The `¬ª¬´` part doesn't do anything but `∆ä` (last three links as a monad) makes it so that if they are deleted an error will occur. Then `·∫°` takes the absolute difference between the result of `¬ª¬´‚Äô∆ä` and the monad `‚Äò}237$` applied to the string. `‚Äò` increments and is a monad, but the `}` turns this into a dyad and applies it to it's right argument, `237`, yielding `238`. Thus `·∫°` yields `0` in the full program.
`¬§` links back to the string literal forming a nilad. The result of this is `0`, so `M` is not applied at all, preventing any error. 
**Possible subprograms:**
* If any part of the string is removed, `<string>..¬§` will be nonzero and `M` gets applied to `0`, causing an error.
* If any part of `L¬ª¬´‚Äô∆ä·∫°‚Äò}237$` is removed either `M` will get applied to `0` or there will be operations between the string and a number, resulting in a `TypeError`.
* If any of `¬§¬°` is removed, `M` gets applied to `0`.
* If the string closing character `‚Äù` and both of `‚Äô‚Äò` get removed and `‚Äú` doesn't, everything after `M` turns into a string so `M` will act on `0`.
	+ If the string closing character `‚Äù` and `‚Äô` get removed and `‚Äú` doesn't, everything between `‚Äù` and `‚Äò` turns into a list of integers.
* If `M` alone is removed there is a an `EOFError` because `¬°` expects a link before the preceding nilad.
* If `M‚Äú` and any number of characters after it is removed, there will be an `EOFError` because the `¬§` looks for a nilad preceding it but doesn't find one. `238` doesn't count because it is part of a monad.
This pretty much covers everything.
I previously hadn't used `¬´¬ª‚Äò` because the latter two cannot be included in the string because they match the `‚Äú` character to form things other than strings. `¬´` can't be in a `‚Äú‚Äù` string either but I don't know why.
[Answer]
# [Python 2](https://docs.python.org/2/), ~~¬†20 21 33 39 45¬†~~ 50 bytes
Now very much a collaborative effort!
+2 thanks to Aidan F. Pierce (replace `sorted({0})` with `map(long,{0})`)
+8 thanks to dylnan (use of `\` and newline to replace space; suggestions to move from `0` to a mathematical expression; replacing `-1` with `-True`; use of hexadecimal)
+11 thanks to Angs (`4*23+~91` -> `~4836+9*1075/2` then later `~197836254+0xbCABdDF` -> `~875+0xDEAdFBCbc%1439/2*6`)
---
```
if\
map(long,{~875+0xDEAdFBCbc%1439/2*6})[-True]:q
```
**[Try it online!](https://tio.run/##K6gsycjPM/r/PzMthis3sUAjJz8vXae6zsLcVNugwsXVMcXNyTkpWdXQxNhS30jLrFYzWjekqDQ11qrw/38A "Python 2 ‚Äì Try It Online")** Or see the [confirmation suite](https://tio.run/##dZJfT8IwFMXf@ymuD6SbGwj@t8lIEGZi4pv6BDyM7YJNoMW2U4jRr45tBwxjSJbs9t5fT3pOu1ybNynON5tcFphQPh2NRmKRLYO5FLP46@f25ipqrwZpr3i470/yRufy4u7s/PT6Oxw2X1SJY/ZOCeFTmKMInEYISeIXGk3VCBmBpeLC1EwMtBT8vUSYrA1qSnCucY/Rh4zPGQgpmocU4Iprc0KJK0wQErLFVSkEFzNw0vDJzRvocqKNHc40KFzIDyxarRbd8fbAVjtVSioNCbRJLkvbT6BDplKBNpkywAWoTMww2B866jgnjkBR1HOPR5245qpWt@2dgxN2/SHz7TFE1dKKsLGbq7XDrCnMAxMSV@W4NJD6H5cCMuvdM1sDjYLRhj90DPajzS6NAd3OKsaj4EhYkD6/9vtpOkgHwALq6DqNyIUAUAXiF3Vo28LCgI6uKGYV9/utOKPWIA0DOtx3u@3xP5XdnS0yG6TLw18QqcLwUfgsybEsdi@l9/i09fH3CR14DOlm8ws "Python 2 ‚Äì Try It Online")
`0xDEAdFBCbc` is hexadecimal and evaluates to `59775106236`.  
`~` is bit-wise complement so `~875` evaluates to `-876`.  
`%` is the modulo operator so `0xDEAdFBCbc%1439` evaluates to `293`.  
`/` is integer division so `0xDEAdFBCbc%1439/2` evaluates to `146`.  
`*` is multiplication so `xDEAdFBCbc%1439/2*6` evaluates to `876`.  
`+` is addition so `~875+xDEAdFBCbc%1439/2*6` evaluates to `0`.  
...no stripped version also evaluates to `0`.
`{0}` is a `set` containing a single element, `0`.
Calling `sorted` with a `set` as the argument yields a list, which may be indexed into with `[...]`.
Without `sorted` the code `({0})` would just yield the `set` and this cannot be indexed into in the same fashion, `if({0})[-True]:q` would raise a `TypeError`.
Indexing in Python is 0-based and allows negative indexing from the back and `True` is equivalent to `1`, hence `sorted({0})[-True]` finds the element `0`, while `sorted({0})[True]` will raise an `IndexError`, as will `sorted({})[-True]` and `sorted({0})[]` is invalid syntax.
The `0` that is found is falsey so the body of the `if`, `q`, is never executed, however if it were it would raise a `NameError` since `q` has not been defined.
Since a non-empty list is truthy we cannot trim down to `if[-1]:q` either.
See the [confirmation suite](https://tio.run/##dZJfT8IwFMXf@ymuD6SbGwj@t8lIEGZi4pv6BDyM7YJNoMW2U4jRr45tBwxjSJbs9t5fT3pOu1ybNynON5tcFphQPh2NRmKRLYO5FLP46@f25ipqrwZpr3i470/yRufy4u7s/PT6Oxw2X1SJY/ZOCeFTmKMInEYISeIXGk3VCBmBpeLC1EwMtBT8vUSYrA1qSnCucY/Rh4zPGQgpmocU4Iprc0KJK0wQErLFVSkEFzNw0vDJzRvocqKNHc40KFzIDyxarRbd8fbAVjtVSioNCbRJLkvbT6BDplKBNpkywAWoTMww2B866jgnjkBR1HOPR5245qpWt@2dgxN2/SHz7TFE1dKKsLGbq7XDrCnMAxMSV@W4NJD6H5cCMuvdM1sDjYLRhj90DPajzS6NAd3OKsaj4EhYkD6/9vtpOkgHwALq6DqNyIUAUAXiF3Vo28LCgI6uKGYV9/utOKPWIA0DOtx3u@3xP5XdnS0yG6TLw18QqcLwUfgsybEsdi@l9/i09fH3CR14DOlm8ws "Python 2 ‚Äì Try It Online") to see: confirmation the bytes being unique; all the errors; and the success of the code itself.
[Answer]
# [C (tcc)](http://savannah.nongnu.org/projects/tinycc), x86\_64, ~~29~~ ~~31~~ ~~33~~ ~~39~~ 40 bytes
```
main[]={(23*8),-~0xABEDFCfebdc%95674+1};
```
Returns **0**. *Thanks to @feersum for suggesting uppercase hex digits.*
[Try it online!](https://tio.run/##S9YtSU7@/z83MTMvOta2WsPIWMtCU0e3zqDC0cnVxc05LTUpJVnV0tTM3ETbsNb6/38A "C (tcc) ‚Äì Try It Online")
### How it works
The assignment writes two ints (**184** and **49664**) to the memory location of *main*. With 32-bit ints and little-endian byte order, the exact bytes are `b8 00 00 00 00 c2 00 00`.
Since tcc doesn't declare the defined array as *.data* (most compilers would), so jumping to main executes the machine code it points to.
* `b8 00 00 00 00` (`mov eax, imm32`) stores the int **0** in the eax register.
* `c2 00 00` (`ret imm16`) pops **0** extra bytes from the stack and returns. (The value in the eax register is the function return value).
[Answer]
# [><>](https://esolangs.org/wiki/Fish), 122 bytes
```
e"~l=?!z6-d0p}xwutsrqonmkjihgfcba`_]\[>ZYXWVUTSRQPONMLKJIHGFEDCB@<:98754321/,+*)('&%$# 
.

	|{Ay
```
[Try it online!](https://tio.run/##S8sszvj/P1WpLsfWXrHKTDfFoKC@tqK8tKS4qDA/Lzc7KzMjPS05KTEhPjYm2i4qMiI8LDQkOCgwwN/P18fby9PD3c3VxdnJwcbK0sLc1MTYyFBfR1tLU0NdTVVFWUFeTlZPRlpKUkJcTFREWEhQgJ@Ph5uTg52NlYWZibGm2rHy/38A "><> ‚Äì Try It Online")
Does nothing. Based on the same format as my [Programming a Pristine World](https://codegolf.stackexchange.com/a/153233/76162) answer. 
First, we check that the length of the code is 122 and error if it isn't. `><>` programs can't end without the use of the `;` command, but if this command is in the program, we can just remove everything before it to make the program end immediately. To combat this, we use the `p` command to place a `;` in the code during runtime. To do this, we subtract 6 from `A` and place it after the `p`.
I'll probably add most of the other values above 127 once I figure out the right two byte values. The missing 5 values are `v^;` and the two newlines.
Of the 7502 sub-programs, 7417 of them errored from invalid instructions, 72 from memory underflow, and 13 from running out of memory.
[Answer]
# JavaScript, 42 bytes
```
if([0XacdCADE*Proxy.length]!=362517948)Áî∞
```
* Removing `i`, `f`, or `if` will cause `SyntaxError: missing ; before statement`;
* Removing `Áî∞` will cause `SyntaxError: expected expression, got end of script`;
* Removing 1 or 2 bytes from `Áî∞` will cause `Invalid or unexpected token`;
* Modify the boolean expression will cause either Syntax Error or Reference Error on `Áî∞`
```
00000000: 6966 285b 3058 6163 6443 4144 452a 5072  if([0XacdCADE*Pr
00000010: 6f78 792e 6c65 6e67 7468 5d21 3d33 3632  oxy.length]!=362
00000020: 3531 3739 3438 29e7 94b0                 517948)...
```
```
(function () {
  let valid = code => { try { eval(code); return true; } catch (e) { return false; } };
  let test = P => {
    for (let i = 0; i < P.length; i++) for (j = i + 1; j <= P.length; j++) {
      let Q = P.slice(0,i) + P.slice(j);
      if (Q && valid(Q)) {
        console.log(Q);
        return false;
      }
    }
    return true;
  };
  let unique = P => !/(.).*\1/.test(P);
  let P = 'if([0XacdCADE*Proxy.length]!=362517948)Áî∞';
  console.log(unescape(encodeURIComponent(P)).length);
  console.log(valid(P));
  console.log(unique(P));
  console.log(test(P));  
}());
```
[Answer]
# [Brain-Flak](https://github.com/DJMcMayhem/Brain-Flak), 2 bytes
```
<>
```
[Try it online!](https://tio.run/##SypKzMzTTctJzP7/38bu/38A "Brain-Flak ‚Äì Try It Online")
Alternatively, `[]`, `{}` or `()`. Removing either bracket causes the other bracket to become unmatched.
Proof that this is the optimal solution:
A Brain-Flak program is made out of nilads (a pair of brackets on their own) or monads (a pair of brackets containing 1 or more nilads). A monad cannot be in a pristine program, as you can simply remove one or more of the nilads. Similarly, you cannot have more than one nilad in the program, since you can remove one of them without breaking the program.
As such, this might be the least optimal language for pristine or unique programming.
[Answer]
# Ada, 110 bytes (latin1)
Probably the best answer you'll get out of any language in use in industry?
Hexdump:
```
0000000: 7061 636b 4167 4520 6266 686a 6c6d 6f71  packAgE bfhjlmoq
0000010: 7274 7576 7778 797a e0e1 e2e3 e4e5 e6e7  rtuvwxyz........
0000020: e8e9 eaeb eced eeef f0f1 f2f3 f4f5 f6f8  ................
0000030: f9fa fbfc fdfe 0d69 730b 656e 6409 4246  .......is.end.BF
0000040: 484a 4c4d 4f51 5254 5556 5758 595a c0c1  HJLMOQRTUVWXYZ..
0000050: c2c3 c4c5 c6c7 c8c9 cacb cccd cecf d0d1  ................
0000060: d2d3 d4d5 d6d8 d9da dbdc ddde 3b0a       ............;.
```
Compile by saving to any file ending in `.ads` and running `gcc -c <filename>`. Produces an executable that does nothing. (Can't provide TIO link since TIO puts code in a `.adb` file and `gcc` by default tries to find a matching spec for them)
Basically declares a package with a name abusing capital/lowercase latin1 letters. Needs a different whitespace character for each of the spaces, so it uses space, CR, LF, and TAB. 
How it looks in vim version:
```
packAgE bfhjlmoqrtuvwxyz√†√°√¢√£√§√•√¶√ß√®√©√™√´√¨√≠√Æ√Ø√∞√±√≤√≥√¥√µ√∂√∏√π√∫√ª√º√Ω√æ^Mis^Kend^IBFHJLMOQRTUVWXYZ√Ä√Å√Ç√É√Ñ√Ö√Ü√á√à√â√ä√ã√å√ç√é√è√ê√ë√í√ì√î√ï√ñ√ò√ô√ö√õ√ú√ù√û;
```
### How it works
In Ada even spec's can be compiled. Spec's are like c's header files, but are more full-featured and can compile some basic code. In order to be valid any specification must have the format: `package <NAME> is ... end <NAME>;` with `<NAME>` matching. The nice thing about Ada is that it is completely case insensitive. Thus as long as your name has uppercase and lowercase variants, you'll be good to go! 
The hard part was getting a compilable unit. Normally Ada programs have a 'main' procedure or function lying outside of any package that will become the final executable. Unfortunately procedures require the `begin` keyword, which leads to too many `e`s (only 2 cases known) while functions require the `return` keyword, which leads to too many `n`s. Thus I had to just compile a package. 
[Answer]
# C, 8 bytes
```
main(){}
```
Does nothing.
[Try it online!](https://tio.run/##S9ZNT07@/z83MTNPQ7O69v9/AA)
[Answer]
# JavaScript, 22 bytes
```
with(0xF?JSON:[])parse
```
[Try it online!](https://tio.run/##y0osSyxOLsosKNHNy09J/f@/PLMkQ8Ogws3eK9jfzyo6VrMgsagYKA4A "JavaScript (Node.js) ‚Äì Try It Online")
### Possible errors
When altered, it will throw one of the following errors1:
```
[some_identifier] is not defined
expected expression, got ')'
expected expression, got ':'
expected expression, got '?'
expected expression, got ']'
expected expression, got end of script
identifier starts immediately after numeric literal
missing ( before with-statement object
missing ) after with-statement object
missing : in conditional expression
missing ] after element list
missing exponent
missing hexadecimal digits after '0x'
missing octal digits after '0o'
unexpected token: ')'
unexpected token: ']'
unexpected token: identifier
```
1. The exact number of distinct errors depends on the engine. This list was generated with SpiderMonkey (Firefox).
[Answer]
# [Python 3](https://docs.python.org/3/) + [Flask-Env](https://pypi.org/project/Flask-Env/), ~~7~~ ~~13~~ ~~14~~ 17 bytes
```
import\
flask_env
```
No TIO because it doesn't have `flask-env`.
Found the longest module name that has no intersection with `import` and doesn't have any numbers at the end of the name. `_sha256` is longer but `256` on it's own doesn't error. I did find one library, `b3j0f.sync` that is one byte longer but I could not get it to import properly.
* +1 byte by replacing a space after `import` with `\<newline>`. Taking out either or both causes an error.
There still may be longer options than `flask_env`, I didn't really do an exhaustive search but I did look through ~70,000 modules. Open to suggestions.
[Answer]
# [R](https://www.r-project.org/), 14 bytes
```
(Sys.readlink)
```
[Try it online!](https://tio.run/##K/r/XyO4slivKDUxJSczL1vz/38A "R ‚Äì Try It Online")
This might be the longest possible in R. Calling any function is doomed to failure, because you would be able to remove everything but the function name, which would just result in printing the function's source code. This is the longest named object in the default R setup with no duplicate characters and no object name left over when removing contiguous characters.
*This first try didn't work, but I learned a lot by trying!*
~~`dontCheck({family;NROW})`~~
[Answer]
# Perl 5, 3 bytes
```
y=>
```
`=>` is the "fat comma," which quotes the bareword on the left. So this is equivalent to
```
"y",
```
which does nothing.
Without the fat comma, `y` is the transliteration operator, which is invalid without three of the same character repeated later.
The fat comma alone is also invalid, as is `=` and `>` alone.
[Answer]
# [brainfuck](https://github.com/TryItOnline/brainfuck), 2 bytes
```
[]
```
[Try it online!](https://tio.run/##SypKzMxLK03O/v8/Ovb/fwA "brainfuck ‚Äì Try It Online")
Inspired by Jo King's [Brain-Flak answer](https://codegolf.stackexchange.com/a/162524/75553). This is optimal because the only error in brainfuck is unmatched brackets. (Again thanks to Jo King for this info.)
[Answer]
# [Ruby](https://www.ruby-lang.org/), 28 bytes
```
(?2*0xA)[%r<\d{1}>].unpack$/
```
[Try it online!](https://tio.run/##KypNqvz/X8PeSMugwlEzWrXIJial2rDWLlavNK8gMTlbRf//fwA "Ruby ‚Äì Try It Online")
[Verify it!](https://tio.run/##rY67boMwFIZn/BQnSStDopiLOlW9qFK7dujQhTAYcxKsUhsdTJQqyrNTIGSqlKnbuf7fR23@03WLWdg2FObahGj2QP0wEXdM2QLhEbj/nCyjw0uQ3tLDpjjGp6dMtKaW6usm5IzpLVB/NlynoS8CsdzEYQauRMM8mVtyPv/AGqXDAlQpSSqHdA8cVkBplAUMTcFYjjvdP@BeVv6QFTDCRrUIbweFtdP2kgb83dK3rEYiIJElwc8ZW0ugQRuIhBi2okKzc@U6hsIyT10s@63QWY8fO72KhVjHGfMmhckh6KszcL44qhO8WmwMdxNxzry/foPEVZHkukjy7yJ16xrgn7LSxQiZ8a77BQ "Verify it!")
[Answer]
# [Standard ML](http://www.mlton.org/), 22 bytes
```
val 1089=op-(765,~324)
```
[Try it online!](https://tio.run/##K87N0c3NKcnP@/@/LDFHwdDAwtI2v0BXw9zMVKfO2MhE8/9/AA "Standard ML (MLton) ‚Äì Try It Online") `op-(a,b)` is the de-sugared form of `a-b`. `~` denotes the unary minus, so we are actually computing `765+324`. This expression is pattern-matched on the constant `1089`. This match succeeds if the program has not been tampered with and does - well, nothing. 
If the match does not succeed because some digits were removed one gets an `unhandled exception: Bind`. Removing `op-` results in a type error because a tuple is matched on an `int`. All other removals should result in an syntax error.
[Answer]
# [Tcl](http://tcl.tk/), 6 bytes
```
puts a
```
[Try it online!](https://tio.run/##K0nO@f@/oLSkWCHx/38A "Tcl ‚Äì Try It Online")
---
# [Tcl](http://tcl.tk/), 3 bytes
```
pwd
```
[Try it online!](https://tio.run/##K0nO@f@/oDzl/38A "Tcl ‚Äì Try It Online")
---
# [Tcl](http://tcl.tk/), 2 bytes
```
cd
```
[Try it online!](https://tio.run/##K0nO@f8/OeX/fwA "Tcl ‚Äì Try It Online")
[Answer]
# Batch, 7 bytes
```
set/px=
```
A nice start
[Answer]
# [Retina](https://github.com/m-ender/retina/wiki/The-Language), 2 bytes
I wouldn't be surprised if this is optimal...
```
()
```
[**Try it online!**](https://tio.run/##K0otycxLNPz/X0Pz/38A "Retina ‚Äì Try It Online")
The regex contains an empty group. Removing either paren will cause a parse error due to unmatched parentheses.
Other solutions are: `\(`, `\)`, `\[`, `\]`, `\*`, `\+`, `\?`, `a]`
[Answer]
# [Malbolge](https://github.com/TryItOnline/malbolge), 76 bytes
```
cba`_^]\[ZYXWVUTSRQPONMLKJIHGFEDCBA@?>=<;:9876543210/.-,+*)('&%$#"!~}|{zyxwd
```
[Try it online!](https://tio.run/##y03MScrPSU/9/z85KTEhPi42JjoqMiI8LDQkOCgwwN/P18fby9PD3c3VxdnJ0cHeztbG2srSwtzM1MTYyNBAX09XR1tLU0NdTVVFWUmxrramuqqyojzl/38A "Malbolge ‚Äì Try It Online")
Malbolge is a great language for this challenge due to the way it translates normalized Malbolge into your familiar keyspam-esque Malbolge.
]