Macro holmes::rule

macro_rules! rule {
    ($holmes:ident, $head_name:ident $head_inner:tt <= $($body_name:ident $body_inner:tt)&*,
   {$(let $bind:tt = $hexpr:tt);*}) => { ... };
    ($holmes:ident, $($head_name:ident $head_inner:tt),* <= $($body_name:ident $inner:tt)&*) => { ... };
    ($($head_name:ident $head_inner:tt),* <= $($body_name:ident $inner:tt)&*) => { ... };
    ($($head_name:ident $head_inner:tt),* <=
   $($body_name:ident $inner:tt)&*, {$(let $bind:tt = $hexpr:tt);*}) => { ... };
}

Adds a Holmes rule to the system

Datalog Rules

rule!(holmes, baz([x], (7)) <= foo((3), [_]) & bar([_], x))

will work as per a normal datalog rule, matching on foo and bar, and generating a baz using any solutions found.

Extended Rules

Holmes rules can also have "where clauses" which call out to native code in the event of a match. For example,

rule!(holmes, baz([y], (8)) <= foo((3), [_]) & bar([_], x), {
  let y = {f(x)}
})

would call the Holmes registered function f on each output of x, bind the result to y, and output it in the first slot of baz.

For more information on the expression and bind syntax, see the hexpr! and bind_match! macro docs.