Argument notation

[webyrd]

Hi Eric!

// Given an edge x -> y, there is a path x -> y.
path(x, y) :- edge(x, y).

// Given an edge x -> z and a path z -> y, there is a path x -> y.
path(x, y) :- edge(x, y: z), path(x: z, y).

I was confused by edge(x, y: z), which seems to match positional argument notation with named arguments. What are the rules for combining named arguments with positional arguments in a call to a relation?

Is this standard Datalog notation, or an extension you added?

Thank you!

Cheers,

--Will

[ekzhang]

Hi Will! There's no positional arguments in Percival; all arguments are named. This is to allow us to do queries on named records, as is common in datasets for machine learning, data science, etc.

In this example, path(x, y) is a shorthand syntax for path(x: x, y: y).

[webyrd]

Thanks, Eric! :)

I think it would be worth explaining this is the tutorial.

Cheers,

--Will

[ekzhang]

Yeah for sure!! Thanks for all the useful feedback :) still have a lot of work to do on the tutorial, haha.