Truth Functional Logic for Hackers

[mcguire]

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/

[tantalor]

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.

[etbebl]

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.

[bbaron63]

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.

[nvader]

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-...

[jonsen]

> 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

?

[hoppp]

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]

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.

[lucaspauker]

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

[cluckindan]

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]

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.