7 ms·

Truth Functional Logic for Hackers

48 points by ChilledTonic 2y ago

tantalor 2y ago
I don't get it. Isn't this what compilers are for? So I don't have to rewrite my code in an equivalent but stupider way just to get a marginal performance gain.
- bbaron63 2y ago
  Presumably, the compiler is not aware of the hardware bug in the OR operation, so it won't do any transforms to avoid using the OR operation.
  - tantalor 2y ago
    Okay so... then patch the compiler? This is basic stuff.
    - spartanatreyu 2y ago
      If it were "basic stuff", then you probably weren't using a high performance compiler to begin with.
- etbebl 2y ago
  I think what you're missing is that the premise of a hardware bug is just a frame story for a lesson in manipulating logical statements, which is the main point.
  - tantalor 2y ago
    Okay, it's just incredibly contrived. You might as well replace "hardware bug" with "a wizard put a curse on the OR operator" or "the president put a tariff on OR imports", and it would be more believable.
mcguire 2y ago
The important part is at the end of the article: "For those interested in building a stronger foundation in logic, the Open Logic Project provides excellent free educational resources on propositional and predicate logic, formal proof systems, and other topics such as modal logic and set theory - all targetted towards a non-mathematical audience." https://openlogicproject.org/ https://openlogicproject.org/
lucaspauker 2y ago
https://en.wikipedia.org/wiki/De_Morgan%27s_laws https://en.wikipedia.org/wiki/De_Morgan%27s_laws
cluckindan 2y ago
The code blocks’ font size varies line by line on mobile. Hint: set it to be smaller than the body text size because monospace fonts tend to be a bit larger than proportional ones.
- ChilledTonic 2y ago
  You've discovered a CSS issue that I did not notice for seven years. Thanks. The issue was that for some reason, different types of code had different font size settings.
hoppp 2y ago
My first thought was to rewrite it without any or and operation. just return early from if statement. If user is blacklisted return access denied; If account is expired return access denied; If no conditions match return access granted; Wouldn't that be more effective?
- ChilledTonic 2y ago
  You are touching on an inherent truth in TFL, which is that there are nearly infinite equivalent statements for any logical sentence. The idea for the article was to make a real example of logical equivalence, as books on the subject stay pretty abstract. - like others have mentioned, in the real world there are smarter choices to be made.
nvader 2y ago
In this blog article from 2021, I warn about making this change without appropriate care, as it has been a source of common bugs: https://danverbraganza.com/writings/de-morgans-flaw-perform-this-refactor-carefully https://danverbraganza.com/writings/de-morgans-flaw-perform-...
- jonsen 2y ago
  > At every place X in the following expression, introduce a boolean negation if there isn’t one (or, equivanently remove one if there is), and I think it should read: At every place X in the following expression, introduce a boolean negation if there isn’t one and remove one if there is, and Maybe even better: At every place X in the following expression, introduce a boolean negation. If you get two concecutive NOT's, they can be removed. Next, I don't see how timespent <= duration is the negation of duration > time_spent ?

48 points by ChilledTonic 2y ago

I don't get it. Isn't this what compilers are for? So I don't have to rewrite my code in an equivalent but stupider way just to get a marginal performance gain.

bbaron63 2y ago
Presumably, the compiler is not aware of the hardware bug in the OR operation, so it won't do any transforms to avoid using the OR operation.
- tantalor 2y ago
  Okay so... then patch the compiler? This is basic stuff.
  - spartanatreyu 2y ago
    If it were "basic stuff", then you probably weren't using a high performance compiler to begin with.
etbebl 2y ago
I think what you're missing is that the premise of a hardware bug is just a frame story for a lesson in manipulating logical statements, which is the main point.
- tantalor 2y ago
  Okay, it's just incredibly contrived. You might as well replace "hardware bug" with "a wizard put a curse on the OR operator" or "the president put a tariff on OR imports", and it would be more believable.

mcguire 2y ago

The important part is at the end of the article: "For those interested in building a stronger foundation in logic, the Open Logic Project provides excellent free educational resources on propositional and predicate logic, formal proof systems, and other topics such as modal logic and set theory - all targetted towards a non-mathematical audience." https://openlogicproject.org/ https://openlogicproject.org/

lucaspauker 2y ago

https://en.wikipedia.org/wiki/De_Morgan%27s_laws https://en.wikipedia.org/wiki/De_Morgan%27s_laws

cluckindan 2y ago

The code blocks’ font size varies line by line on mobile. Hint: set it to be smaller than the body text size because monospace fonts tend to be a bit larger than proportional ones.

ChilledTonic 2y ago
You've discovered a CSS issue that I did not notice for seven years. Thanks. The issue was that for some reason, different types of code had different font size settings.

hoppp 2y ago

My first thought was to rewrite it without any or and operation. just return early from if statement. If user is blacklisted return access denied; If account is expired return access denied; If no conditions match return access granted; Wouldn't that be more effective?

ChilledTonic 2y ago
You are touching on an inherent truth in TFL, which is that there are nearly infinite equivalent statements for any logical sentence. The idea for the article was to make a real example of logical equivalence, as books on the subject stay pretty abstract. - like others have mentioned, in the real world there are smarter choices to be made.

nvader 2y ago

In this blog article from 2021, I warn about making this change without appropriate care, as it has been a source of common bugs: https://danverbraganza.com/writings/de-morgans-flaw-perform-this-refactor-carefully https://danverbraganza.com/writings/de-morgans-flaw-perform-...

jonsen 2y ago
> At every place X in the following expression, introduce a boolean negation if there isn’t one (or, equivanently remove one if there is), and I think it should read: At every place X in the following expression, introduce a boolean negation if there isn’t one and remove one if there is, and Maybe even better: At every place X in the following expression, introduce a boolean negation. If you get two concecutive NOT's, they can be removed. Next, I don't see how timespent <= duration is the negation of duration > time_spent ?