4 ms·

Wait until you hear about Common Lisp’s string formatter.

• hnlmorg 5mo ago
  Want to share some details?
  • bandrami 5mo ago
    The FORMAT directive is Turing-complete. The full spec is here: https://www.lispworks.com/documentation/HyperSpec/Body/22_c.htm https://www.lispworks.com/documentation/HyperSpec/Body/22_c....
    • hnlmorg 5mo ago
      printf is also Turing complete. Thanks for the link, I'll have a read of that later
      • db48x 5mo ago
        `printf` with some GNU extensions is accidentally Turing–complete because you can overwrite it's internal state. Common Lisp’s `format` is intentionally and safely Turing–complete because it includes directives for conditionals, iteration, goto, and recursion. The classic example for printing lists: (setq foo "Items:~#[ none~; ~S~; ~S and ~S~ ~:;~@{~#[~; and~] ~S~^ ,~}~].") (format nil foo) => "Items: none." (format nil foo 'foo) => "Items: FOO." (format nil foo 'foo 'bar) => "Items: FOO and BAR." (format nil foo 'foo 'bar 'baz) => "Items: FOO, BAR, and BAZ." (format nil foo 'foo 'bar 'baz 'quux) => "Items: FOO, BAR, BAZ, and QUUX." <https://www.lispworks.com/documentation/HyperSpec/Body/22_cgb.htm https://www.lispworks.com/documentation/HyperSpec/Body/22_cg...> The directives for recursion takes a format string and a list, calls `format` on the string using the list as the list of arguments and then inserts the result into the current output. This is much less verbose than calling `snprintf` to create a temporary string and then insertimg it into the current output with %s. <https://www.lispworks.com/documentation/HyperSpec/Body/22_cgf.htm https://www.lispworks.com/documentation/HyperSpec/Body/22_cg...> There is also a directives for calling a Lisp function to print the next argument, and the standard library includes several functions intended to be called from within a format string. <https://www.lispworks.com/documentation/HyperSpec/Body/22_ced.htm https://www.lispworks.com/documentation/HyperSpec/Body/22_ce...>