No relation to the sports channel.

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Joined 2 years ago
Cake day: June 9th, 2023
  • fubo@lemmy.worldtoProgramming@programming.dev•Common Misconceptions about Compilers
    202·
    7 days ago
    • The compiler hates you
    • The compiler sees nothing wrong with your code and is just giving error messages to look busy
    • The compiler was written by a maniac with a semicolon fixation
    • The compiler could optimize your code, but it’s just not feeling it today
    • The compiler wonders why you can’t match braces right like your brother does
    • The compiler had a torrid affair with a Perl interpreter in 2006
    • The compiler likes big butts and cannot lie
    • The compiler wants to grow up to be an IDE but hasn’t told its parents they need to send it to GUI school yet
    • The compiler reads Nazis on Twitter but only to make fun of them
    • The compiler works for the Servants of Cthulhu
  • fubo@lemmy.worldtoProgrammer Humor@lemmy.ml•Oh boy what a beautiful regex. I'm sure it does something logical and easy to understand.
    12·
    2 months ago

    Regex is good for a few very specific things, and sysadmins used to use it for goddamn everything. If all your server logs are in lightly-structured text files on a small number of servers, being able to improvise regex is damn useful for tracking down server problems. Just write a shell loop that spawns an ssh logging into each server and running grep over the log files, to look for that weird error.

    These days, if you need to crunch production server logs you probably need to improvise in SQL and jq and protobufs or systemd assmonkery or something.

    But if you actually need a parser, for goodness sake use a parser combinator toolkit, don’t roll your own, especially not with regex. Describing your input language in plain Haskell is much nicer than kludging it.

    (This is the “totally serious software engineering advice” forum, right?)

  • fubo@lemmy.worldtoProgrammer Humor@lemmy.ml•Oh boy what a beautiful regex. I'm sure it does something logical and easy to understand.
    135·
    2 months ago

    The answer given in the spoiler tag is not quite correct!

    Test case

    According to the spoiler, this shouldn’t match “abab”, but it does.

    Corrected regex

    This will match what the spoiler says: ^.?$|^((.)\2+?)\1+$

    Full workup

    Any Perl-compatible regex can be parsed into a syntax tree using the Common Lisp package CL-PPCRE. So if you already know Common Lisp, you don’t need to learn regex syntax too!

    So let’s put the original regex into CL-PPCRE’s parser. (Note, we have to add a backslash to escape the backslash in the string.) The parser will turn the regex notation into a nice pretty S-expression.

    > (cl-ppcre:parse-string "^.?$|^(..+?)\\1+$")
(:ALTERNATION
 (:SEQUENCE :START-ANCHOR (:GREEDY-REPETITION 0 1 :EVERYTHING) :END-ANCHOR)
 (:SEQUENCE :START-ANCHOR
  (:REGISTER
   (:SEQUENCE :EVERYTHING (:NON-GREEDY-REPETITION 1 NIL :EVERYTHING)))
  (:GREEDY-REPETITION 1 NIL (:BACK-REFERENCE 1)) :END-ANCHOR))

    At which point we can tell it’s tricky because there’s a capturing register using a non-greedy repetition. (That’s the \1 and the +? in the original.)

    The top level is an alternation (the | in the original) and the first branch is pretty simple: it’s just zero or one of any character.

    The second branch is the fun one. It’s looking for two or more repetitions of the captured group, which is itself two or more characters. So, for instance, “aaaa”, or “abcabc”, or “abbaabba”, but not “aaaaa” or “abba”.

    So strings that this matches will be of non-prime length: zero, one, or a multiple of two numbers 2 or greater.

    But it is not true that it matches only “any character repeated a non-prime number of times” because it also matches composite-length sequences formed by repeating a string of different characters, like “abcabc”.

    If we actually want what the spoiler says — only non-prime repetitions of a single character — then we need to use a second capturing register inside the first. This gives us:

    ^.?$|^((.)\2+?)\1+$.

    Specifically, this replaces (..+?) with ((.)\2+?). The \2 matches the character captured by (.), so the whole regex now needs to see the same character throughout.

  • fubo@lemmy.worldtoWorld News@lemmy.ml•Majority of Americans and Europeans support ending the war in Ukraine
    1912·
    7 months ago

    I’m for ending the war through a unilateral surrender of Russian forces and the trial of Mr Putin for crimes against humanity. However, my opinion doesn’t have a lot of influence over whether that happens.

    Similarly, I’m for ending the war in Gaza through the voluntary disarmament of Hamas, the repudiation of terrorism as a way of life, the handover of illegal settlements to displaced Palestinian Arab civilians, and the prosecution of Netanyahu for treason and war crimes. But I don’t expect to get to make that decision either.

  • fubo@lemmy.worldtoProgramming@programming.dev•White House: Future Software Should Be Memory Safe
    188·
    10 months ago

    Rust does memory-safety in the most manual way possible, by requiring the programmer prove to the compiler that the code is memory-safe. This allows memory-safety with no runtime overhead, but makes the language comparatively difficult to learn and use.

    Garbage-collected compiled languages — including Java, Go, Kotlin, Haskell, or Common Lisp — can provide memory-safety while putting the extra work on the runtime rather than on the programmer. This can impose a small performance penalty but typically makes for a language that’s much easier on the programmer.

    And, of course, in many cases the raw performance of a native-code compiled language is not necessary, and a bytecode interpreter like Python is just fine.