4 ms·

I always thought, maybe because of C, that \0??? is an octal escape; so in my mind \012 is \x0a or 0x0a, and \010 is 0x08. So I find this quite confusing; mayb

by tzot 2y ago

I always thought, maybe because of C, that \0??? is an octal escape; so in my mind \012 is \x0a or 0x0a, and \010 is 0x08. So I find this quite confusing; maybe OCaml does not have octal escapes but decimal ones, and \09 is the Tab character. I haven't checked.

dpassens 2y ago
It is indeed a decimal escape: https://ocaml.org/manual/5.2/lex.html#char-literal https://ocaml.org/manual/5.2/lex.html#char-literal
fanf2 2y ago
Yeah backslash-decimal character escapes are really rare, the only string syntaxes I know of that have them are in O’Caml, Lua, and DNS
- binary132 2y ago
  Is O’Caml an Irish fork of OCaml? :)
  - fanf2 2y ago
    It was the spelling when I first learned the language, eg https://arxiv.org/pdf/2006.05862 https://arxiv.org/pdf/2006.05862 https://caml.inria.fr/pub/old_caml_site/FAQ/stephan.html https://caml.inria.fr/pub/old_caml_site/FAQ/stephan.html
    - binary132 2y ago
      Oh, interesting. Thanks for sharing
syncsynchalt 2y ago
There's some truth in that direction, but it's not related to backslash escapes (which are symbolic/mnemonic, \n is "[Ne]wline", \r is "carriage [R]eturn", \t is "[T]ab", and so on). Instead, consider the convention of control characters, such as ^C (interrupt), ^G (bell), or ^M (carriage return). Those are characters in the C0 control set, where ^C is \0x3, ^G is \0x7, or ^M is \0xD. You're seeing a bit of cleverness that goes back to pre-Unix days: to represent the invisible C0 characters in ASCII, a terminal prepends the "^" character and prints the character AND-0x40, shifting it into a visible range. You may want to pull up an ASCII table such as https://www.asciitable.com https://www.asciitable.com to follow along. Each control character (first column) is mapped to the ^character two columns over, on that table. That's why \0 is represented with the odd choice of ^@, the escape key becomes ^[, and other hard-to-remember equivalents. These weren't choices made by Unix authors, they're artifacts of ASCII numbering.
- sudobash1 2y ago
  Minor nitpick: the terminal prints the character OR'ed with 0x40 (not AND'ed).
  - syncsynchalt 2y ago
    Oop. I always make the same mistake in code too.
- wruza 2y ago
  Better visible here: https://www.commfront.com/pages/ascii-chart https://www.commfront.com/pages/ascii-chart

by tzot 2y ago

dpassens 2y ago

It is indeed a decimal escape: https://ocaml.org/manual/5.2/lex.html#char-literal https://ocaml.org/manual/5.2/lex.html#char-literal

fanf2 2y ago

Yeah backslash-decimal character escapes are really rare, the only string syntaxes I know of that have them are in O’Caml, Lua, and DNS

binary132 2y ago
Is O’Caml an Irish fork of OCaml? :)
- fanf2 2y ago
  It was the spelling when I first learned the language, eg https://arxiv.org/pdf/2006.05862 https://arxiv.org/pdf/2006.05862 https://caml.inria.fr/pub/old_caml_site/FAQ/stephan.html https://caml.inria.fr/pub/old_caml_site/FAQ/stephan.html
  - binary132 2y ago
    Oh, interesting. Thanks for sharing

syncsynchalt 2y ago

There's some truth in that direction, but it's not related to backslash escapes (which are symbolic/mnemonic, \n is "[Ne]wline", \r is "carriage [R]eturn", \t is "[T]ab", and so on). Instead, consider the convention of control characters, such as ^C (interrupt), ^G (bell), or ^M (carriage return). Those are characters in the C0 control set, where ^C is \0x3, ^G is \0x7, or ^M is \0xD. You're seeing a bit of cleverness that goes back to pre-Unix days: to represent the invisible C0 characters in ASCII, a terminal prepends the "^" character and prints the character AND-0x40, shifting it into a visible range. You may want to pull up an ASCII table such as https://www.asciitable.com https://www.asciitable.com to follow along. Each control character (first column) is mapped to the ^character two columns over, on that table. That's why \0 is represented with the odd choice of ^@, the escape key becomes ^[, and other hard-to-remember equivalents. These weren't choices made by Unix authors, they're artifacts of ASCII numbering.

sudobash1 2y ago
Minor nitpick: the terminal prints the character OR'ed with 0x40 (not AND'ed).
- syncsynchalt 2y ago
  Oop. I always make the same mistake in code too.
wruza 2y ago
Better visible here: https://www.commfront.com/pages/ascii-chart https://www.commfront.com/pages/ascii-chart