Bootstrap

Files: quilt/src/langs/bootstrap/, bin/bootstrap, bin/bootstrap0, bin/bootstrap1

Quilt is self-hosting: the Rust MetaLanguage implementation (langs/rust/meta.rs) is generated by a Quilt program (langs/bootstrap/mk_meta.rs.quilt), not hand-written. This page explains how that works.

Why bootstrap?

RustMetaLanguage expands Rust .quilt files. To expand mk_meta.rs.quilt (which contains ⟨T⟩ type placeholders and quote/unquote syntax) we need some MetaLanguage first. The Bootstrap meta-language serves this role: it works without meta.rs and uses a slower string-based lifting strategy (strlift.rs).

The two stages

Both stages run the same generator program via quilt, mk_meta.rs.quilt. The program:

1. Uses the Quilt library (use quilt::prelude::*;) to build RustMetaLanguage's implementation as a QTerm.
2. Uses ⟨T⟩ (expanded to Arc<QTerm>) to avoid hard-coding the type.
3. Writes quilt/src/langs/rust/meta.rs and runs cargo fmt on it.

The stages differ only in which MetaLanguage expands the generator.

Stage 0 — bootstrap0

Expand and run mk_meta.rs.quilt using the Bootstrap multi (BootstrapMetaLanguage), with the CLI built --no-default-features -F bootstrap:

cd quilt && cargo run -p quiltlang --no-default-features -F bootstrap -- -m bootstrap src/langs/bootstrap/mk_meta.rs.quilt

This works without an existing meta.rs and regenerates it.

Stage 1 — bootstrap1

Expand and run mk_meta.rs.quilt again, this time with the Omni multi — i.e. the freshly generated RustMetaLanguage (self-hosting):

cd quilt && cargo run -p quiltlang --no-default-features -F rust,parse -- -m omni src/langs/bootstrap/mk_meta.rs.quilt

bootstrap (no suffix) runs stage 0 then stage 1. If meta.rs is already correct and nothing has changed in mk_meta.rs.quilt, both stages leave the file unchanged (idempotent).

mk_meta.rs.quilt

This is a Rust source file (a rust-script script) that uses:

• ⟨T⟩ for every occurrence of Arc<QTerm> (expanded by bootstrap → Arc<QTerm>).
• ↖…↗ to quote the body of meta.rs (so the Quilt machinery generates the file's content as a QTerm).

The structure is roughly:

#!/usr/bin/env rust-script
use quilt::prelude::*;
use quilt::term::STerm;

fn main() -> Result<()> {
    let meta: ⟨T⟩ = ↖
        // ... full RustMetaLanguage impl body ...
        // uses ⟨T⟩ for Arc<QTerm> again inside the quote
    ↗;
    meta.dump_with_cmds("src/langs/rust/meta.rs", …)?;
    // cargo fmt
    Ok(())
}

BootstrapMetaLanguage

File: langs/bootstrap/meta.rs

Implements MetaLanguage using the string-lift strategy from strlift.rs instead of the direct-builder strategy in langs/rust/ops.rs. Specifically, expand_tuple calls strlift::bs_lift which renders the entire sub-tree to a string and re-parses it. This is slower and less structured, but avoids the circular dependency on RustMetaLanguage.

The operator spellings for bootstrap differ from the production Rust spellings:

Glyph	Bootstrap	Rust (production)
↑	"bs_lift()"	"qlift()"
↓	"bs_reduce()"	"reduce()"
⟨T⟩	"Arc<QTerm>"	(via bootstrap output)
⟨N⟩	"bs_name()"	"name()"

Bootstrap multi type

pub type Bootstrap = Multi<Singleton<BootstrapRustLanguage>, Singleton<BootstrapMetaLanguage>>;

BootstrapRustLanguage is RustLanguage under the hood — bootstrap re-uses the production Rust parser. The Multi CLI argument -m bootstrap selects this multi.

Idempotency

A clean run of bootstrap leaves meta.rs byte-for-byte unchanged. This is verified in CI by checking that the file has no diff after running bootstrap. If meta.rs diverges, it means a change to mk_meta.rs.quilt or a breaking change in ops.rs that must be reconciled.

What else could be bootstrapped

meta.rs is currently the only generated file. The Dogfooding Audit surveys the rest of the tree for code that is hand-written but could be produced the same way — and, just as usefully, the places where it should not be.