The r7rs (scheme time) library, supplied as a host library.

This module is a worked example of an embeddable Schooner library — an Elixir module that builds a Schooner.Library.t/0 via Schooner.Host.library/1. The library is not in Schooner's default standard registry; embedders opt in by listing it on Schooner.Environment.new/1:

env =
  Schooner.Environment.new(
    libraries: [Schooner.Time.library()]
  )

Schooner.eval!("(import (scheme time)) (current-second)", env)
# => 1745234567.123456

The name (scheme time) is the canonical r7rs name; scripts opt in the spec-conformant way with (import (scheme time)). Because the library is not pre-registered, an embedder who does not list it preserves the "default sandbox is pure" property — wall-clock access has to be deliberately granted.

Why a host library, not a baked-in primitive

Every primitive Schooner ships in (scheme base), (scheme inexact), and friends is pure and deterministic. Time is the first side-effecting binding: it leaks wall-clock state into the script and breaks reproducibility. Keeping it out of the default registry and shipping it as a separately-opt-in host library matches the trust model documented in Sandbox.

Authoring this as a host library — instead of as one more Schooner.Primitives.* module — also makes it a worked reference for embedders writing their own libraries. The shape here is the shape recommended in Host Functions:

1. A single public library/0 (or library/1 if the host needs to inject configuration) that returns a %Schooner.Library{}.
2. Internal primitive implementations follow the standard (list(Schooner.Value.t()) -> Schooner.Value.t()) ABI.
3. The library name is canonical (["scheme", "time"] here), which makes it sandbox-safe — the script must (import ...) to reach it.

Copy this file as a starting point for any embeddable library that needs to expose host capabilities to Scheme.

Procedures

All three procedures are r7rs §6.13:

• (current-second) — inexact seconds since the epoch. Backed by :os.system_time(:nanosecond) / 1.0e9. R7RS specifies TAI seconds; Schooner returns POSIX seconds, matching what every mainstream Scheme implementation actually does (Chibi, Racket, Guile).

• (current-jiffy) — exact monotonic integer. Backed by :erlang.monotonic_time/0. The absolute value is unspecified and may be negative; only differences between two current-jiffy calls in the same VM are meaningful.

• (jiffies-per-second) — exact integer giving the resolution of current-jiffy. Backed by :erlang.convert_time_unit(1, :second, :native). Expected idiom: divide a jiffy difference by this to get seconds.