065 phantom compound unit

// Test: compound phantom labels carry the result of dimensional arithmetic.
//
// `i32[meter]` divided by `i32[second]` returns `i32[meter/second]`. The
// phantom checker doesn't derive that relationship — the author declares it
// in the converter event's signature. The `/` in the label is just opaque
// characters; what makes it meaningful is that a producer event has it as
// an output and that producer's input/output declarations match physical
// units.

import std/io

event read-distance { trip_id: u8 } -> i32<meter>

read-distance -> 100

event read-time { trip_id: u8 } -> i32<second>

read-time -> 4

event compute-velocity { d: i32<meter>, t: i32<second> } -> i32<meter/second>

compute-velocity -> d / t

read-distance(trip_id: 1): m |> read-time(trip_id: 1): s |> compute-velocity(d: m, t: s): v |> std/io:print.ln("{{ v:d }} m/s")