003 trellis check categorize

// TEST: std/trellis — CATEGORIZATION surface: check-as-dispatch.
//
// Where `enforce` is a law (violation = compile error), `check` is a
// QUESTION: does the program match this trellis? The answer arrives as
// ordinary branch dispatch — `| ok |>` / `| error msg |>` — resolved at
// comptime (the trellis library computes the verdict in Stage C and the
// losing branch is dead code by construction).
//
// This is the capability-float substrate: the same mechanism, invoked by
// the compiler rather than the user, lets variant selection ask "is this
// flow gpu-legal? simd-fusable?" and float the best variant whose trellis
// the flow satisfies — early warning instead of generated-code wreckage.
//
// This program conforms to "kernel-shape", so the ok branch fires.

~import std/trellis
~import std/kernel
~import std/io

~std/trellis:define("kernel-shape")
| `std/kernel:init/kernel/.*` _ => ok
| `.*std/kernel:pairwise` _ => error "std/kernel:pairwise found outside std/kernel:init"
| `.*std/kernel:self` _ => error "std/kernel:self found outside std/kernel:init"

~std/kernel:shape(Body) {
    mass: f64,
}

~std/kernel:init(Body) {
    { mass: 1.0 },
    { mass: 2.0 },
}
| kernel k |> std/kernel:self { k.mass *= 2.0 }
| computed c |> std/io:print.blk {
        mass[0]={{ c[0].mass:f }} mass[1]={{ c[1].mass:f }}
    }

~std/trellis:check("kernel-shape")
| ok |> std/io:print.ln("categorized: kernel-shape")
| error msg |> std/io:print.ln(msg)