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.