5843503033
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_015f73FesGZGYPkmDvUcj6QX
81 lines
4.4 KiB
Markdown
81 lines
4.4 KiB
Markdown
# Finch, for SchOS's own programs
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**Two things, and only one of them is later.**
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- *Bringing Finch into SchOS* (below) is **later** — behind [1.0.md](1.0.md)'s
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freeze like everything else here that is not named there.
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- *Finishing Finch itself*, and making it fully self-hosting, is work on the
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Finch repository and does not touch this tree. It can proceed now; see
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[the gap](#the-self-hosting-gap).
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Finch is the author's own language: <https://pandor.pl/git/nexoniarz/Finch>
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(GitHub mirror: `Nexoniarz/Finch`). The plan is to write SchOS's own
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applications and tools in it, in place of C, and so leave behind what C does
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badly: silent narrowing, signed/unsigned mixing, undefined behaviour on an
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out-of-range index, a forgotten `free`.
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## What it is today (version 2.4.0)
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Measured from the repository, not from its README alone:
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- **LLVM front end**, C-like syntax, no semicolons, no headers, no preprocessor.
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It compiles through LLVM's `-O2` pipeline to native code; there is no
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garbage collector.
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- **Values, not references:** lists, text and structs copy on assignment and
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are freed at the end of their block. Out-of-range indexes, division by zero
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and null pointers stop with a runtime error rather than undefined behaviour.
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- **Errors as values** (`int(s) or 0`, `try read_file(p)`), maps, methods,
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modules.
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- **C interop through libclang:** `import "foo.h"` plus `link "foo"` calls any C
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library, structs by value and callbacks included. That is the way in to
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everything SchOS already has — musl, the `/dev/*` interfaces, Alpine's
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libraries.
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- **Targets:** Linux, macOS, Windows, on x86-64 and ARM64 (`src/platform.fch`;
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the System V, AAPCS64 and Microsoft x64 ABIs are in `src/gen.fch`). ARM64 and
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Windows programs are run under qemu and Wine in the tests; macOS is IR-checked.
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- **Language:** enums, `match`, generics, errors as values, maps, methods,
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`defer`, and a standard library in Finch (`json`, `path`, `time`, `proc`).
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- **Tooling:** a language server (`finch lsp`, written in Finch), VS Code and
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Kate support, 107 tests.
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- **Written in itself:** the whole compiler is Finch (about 8,500 lines in
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`src/`, no C++) and builds itself from a committed seed to a byte-identical
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result — `bootstrap/build.sh`.
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## What SchOS would need to do
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1. **A `schos` target.** `finch` picks a triple, a C compiler and a linker per
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target. SchOS runs unmodified Alpine binaries and Alpine's musl
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(see [alpine.md](alpine.md)), so the first target is **the existing
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`x86_64-unknown-linux-musl`**, and a Finch program built on the host should
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run on SchOS before anything in Finch is made SchOS-specific. Test that
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before writing a line of target code.
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2. **The compiler on SchOS.** Needs LLVM 21 and libclang, both of which Alpine
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packages. That is a question of apk and memory, not of SchOS.
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3. **The Finch-written compiler on SchOS.** It emits LLVM IR as text and needs
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only `clang` and libclang, no LLVM C++ libraries, so it is the compiler that
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would ship in the image. It needs a seed made for the SchOS target.
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4. **Bindings** for SchOS's own interfaces (`/dev/pci`, `/dev/netdev`,
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schinit's job protocol, the framebuffer) — generated by the C importer from
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the headers in `include/uapi/`, so they are not hand-written and cannot
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drift from the kernel.
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## Where self-hosting stands
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The compiler is written in Finch and nothing else. `bootstrap/build.sh` builds it
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from the seed (its own IR, Linux x86-64 and ARM64) and then from itself, and
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checks the two make identical IR. It passes the 107 tests: programs, refusals,
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`-g` builds, a shared library and the language server. The work is on the
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`finish-finch` branch of `github.com/Nexoniarz/Finch`; `before-bootstrap` there
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is the all-C++ compiler, kept as the backup. `main` is untouched.
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Left: the compiler does not run on macOS or Windows yet (it needs a seed made
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with those systems' headers; programs for them are built from Linux with
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`--target`), and `main` is switched to this branch only when the author says so,
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after merging their local `embed` work.
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## Rules
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- Inference, not an instruction: the kernel stays in C. Finch is for
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applications and tools; the user said "our apps or stuff like that".
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- No new capability starts until [the register of unfinished work](1.0.md#the-freeze-and-the-register-of-unfinished-work)
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is empty; the SchOS half of this document is a plan, not an exception to that.
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