tromp an hour ago

The author presents most known numeral systems (ways of representing natural numbers) in lambda calculus, classified by whether the term use their bound variables exactly one time (linear), at most one time (affine), or multiple times (non-linear). Mackie's paper [0] (one of the references) provides a good introduction to these.

He illustrates some numerals in each system with a graphical notation that strongly reminds me of interaction nets [1], a computational model closely related to lambda calculus. The notation they use for lambda terms is rather non-standard. Compare

> In β-reduction, k[(x⇒b)←a]⊳k[b{a/x}]k[(x⇒b)←a]⊳k[b{a/x}]

with Wikipedia's [2]

> The β-reduction rule states that a β-redex, an application of the form (λx. t) s, reduces to the term t[x:=s].

The k[...] part means that β-reduction steps can happen in arbitrary contexts.

[0] https://www.researchgate.net/publication/323000057_Linear_Nu...

[1] https://en.wikipedia.org/wiki/Interaction_nets

[2] https://en.wikipedia.org/wiki/Lambda_calculus

lefra 2 hours ago

I think I lack context to see what this is about. The line graphs are pretty though, and I'd like to understand more.

Sharlin 43 minutes ago

The author unfortunately only describes about half of the syntax they use, or rather, they describe the syntax of the language but assume the reader is familiar with the (rather obscure even in a PLT context) metalanguage.

p1esk 3 hours ago

I didn’t understand that notation. Can someone please explain?

  • ngruhn 2 hours ago

    I think:

       x => a
    
    is:

       λx. a 
    
    and

       f <- a
    
    is just application. I.e.

       f a
    • lefra 2 hours ago

      What about big T, square/angle brackets, and braces?

      • ngruhn 2 hours ago

        yeah no idea

  • jdw64 44 minutes ago

    const f = (x) => x + 1;

throwaway81523 an hour ago

Hmm nice I guess, but I expected it was going to be about transfinite ordinals. I wonder if it can be extended to them.