HIR

The HIR (high-level IR) is the first semantically-shaped view of a Mighty program. It is name-resolved (slice 1: per-file scope), arena- allocated, and indexed by stable Idx<_> ids.

It lives in crates/mty-hir/.

Storage shape

A whole package is a single Package struct with one arena per node kind:

pub struct Package {
    pub items: Arena<Item>,
    pub fns: Arena<HirFn>,
    pub structs: Arena<HirStruct>,
    pub enums: Arena<HirEnum>,
    pub type_aliases: Arena<HirTypeAlias>,
    pub agents: Arena<HirAgent>,
    pub protocols: Arena<HirProtocol>,
    pub supervisors: Arena<HirSupervisor>,
    pub exprs: Arena<HirExpr>,
    pub pats: Arena<HirPat>,
    pub types: Arena<HirType>,
    pub blocks: Arena<HirBlock>,
    pub locals: Arena<HirLocal>,
    pub top_level: Vec<ItemId>,
}

Ids are typed la-arena indices:

pub type ItemId = Idx<Item>;
pub type FnId   = Idx<HirFn>;
pub type ExprId = Idx<HirExpr>;
// ... and so on for every arena

This shape is good for cheap cloning, snapshot dumping, and incremental analysis in later slices. It is bad for graph-shaped mutations; those are intentionally pushed into later IRs (AIR, MtyIR).

Lowering entry

LoweringCtx::new()
    .lower_file(file: sdust_ast::File)
    -> (Package, Vec<Diagnostic>)

LoweringCtx owns the in-flight Package and the diagnostics vector. It exposes per-arena alloc_* helpers and dispatches per-kind lowering through submodules:

Submodule	What it lowers
lower/items.rs	fn, struct, enum, type alias, impl, trait, use, mod, const, extern, export, macro
lower/agents.rs	agent, protocol, supervisor, on-handler, on_fail, child
lower/exprs.rs	every HirExpr variant
lower/patterns.rs	every HirPat variant
lower/types.rs	path, borrow, tuple, array, fn, T!E result sugar, T!{A,B} union

Desugarings performed

Slice 1 normalizes a small set of surface forms:

• T!E becomes HirType::Result { ok: T, err: E }. T!{A,B} becomes HirType::Result { ok, err: HirType::Union([A, B]) }. The original surface form is preserved on the CST so the formatter can re-emit it.
• Expression-body functions (fn f() = expr) lower to a block with a single tail expression.
• The compact agent forms (on Msg(args) -> body, agent state without an explicit state keyword) lower to the same HirAgent shape as the long form.

Dumping

dump::dump_package(&pkg) -> String returns a stable S-expression form, used by snapshot tests and the mty dump --hir command.

Resolve

The resolve.rs module is a stub in slice 1. Real cross-file name resolution lands in slice 3.

See also

• Architecture
• Diagnostics