7a9db03bcc
declare now takes the type's NAME — `declare(name) -> Type` — because the
compiler needs it at compile time to register the forward type, which is
what makes self-reference resolve. EnumInfo drops `name` (it lives on
declare now); define completes the handle's body in place (the slot is
already named).
Self-reference mechanism (evalComptimeType): before lowering a comptime
type expression, preregisterForwardTypes scans it (and a called ctor fn's
body) for `declare("Name")` calls and registers each as an empty forward
nominal type AND binds it as a type alias. The alias is essential: a
`Name :: ctor()` decl makes `Name` a const_decl author, so a `*Name`
self-reference resolves through the forward-ALIAS path
(type_aliases_by_source), which a bare findByName registration doesn't
satisfy. With both in place `*Name` resolves to the forward slot at lower
time; the interp's declare returns that same slot; define fills it.
List :: make_list();
make_list :: () -> Type {
h := declare("List");
return define(h, .enum(.{ variants = .[
EnumVariant.{ name = "cons", payload = *List },
EnumVariant.{ name = "nil", payload = void } ] }));
}
Verified: cons/nil construct + match (direct and through the pointer),
multi-node list traversal via a recursive `count(*List)`. meta.sx
RecvResult/TryResult + examples 0614/0615/0617 updated to declare(name);
full suite green (673).
77 lines
3.7 KiB
Plaintext
77 lines
3.7 KiB
Plaintext
// Comptime type metaprogramming — `declare` / `define` (construct a NEW nominal
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// type from data), plus `type_info` / `field_type` (reflect a type → data) and
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// the data model they reflect INTO and construct FROM.
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//
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// This is a SEPARATE on-demand module rather than part of the prelude: its data
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// types would otherwise intern into every module's type table and shift every
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// `.ir` snapshot. Import it explicitly: #import "modules/std/meta.sx";
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//
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// All four are comptime-only builtins — reaching one at runtime is a hard error
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// (the type must be minted / reflected at compile time).
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// One variant of a constructed enum: a name plus an optional payload type.
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// `payload = void` means a tagless variant (e.g. `closed`).
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EnumVariant :: struct {
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name: string;
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payload: Type;
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}
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// The shape of an enum/tagged-union being reflected or constructed. The type's
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// NAME is supplied to `declare(name)`, not here — `declare` needs it at compile
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// time to register the forward type so the body can reference itself (`*Name`).
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EnumInfo :: struct {
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variants: []EnumVariant;
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}
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// The reflected/constructed type shape. A tagged union over the kinds of type
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// that can be minted. Only `` .`enum `` ships today; struct/tuple land later.
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// The variant uses the backtick raw-identifier escape so it reads as the
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// keyword `enum` (`` .`enum(...) ``) rather than a mangled `enum_`.
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TypeInfo :: enum {
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`enum: EnumInfo;
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}
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// The compiler's ONLY type-construction primitives (comptime-only #builtins):
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// declare(name) — mint a NEW empty (undefined) nominal type NAMED
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// `name`, returned as a `Type` handle. The compiler
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// registers the forward type at compile time, so the
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// body of `define` can reference it BY NAME — that's how
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// self-reference works (`payload = *List` resolves to the
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// forward `List`). Using the type before its `define` is
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// a loud error; a pointer to it is fine.
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// define(handle, info) — fill a declared handle's body from a `TypeInfo`, and
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// RETURN the handle so the one-shot form chains:
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// List :: define(declare("List"), .enum(.{ variants = .[
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// EnumVariant.{ name = "cons", payload = *List },
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// EnumVariant.{ name = "nil", payload = void } ] }));
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declare :: (name: string) -> Type #builtin;
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define :: (handle: Type, info: TypeInfo) -> Type #builtin;
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type_info :: ($T: Type) -> TypeInfo #builtin;
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field_type :: ($T: Type, idx: i64) -> Type #builtin;
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// --- Type constructors built in sx library code (no compiler machinery) ---
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//
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// The channel result types, expressed as type-fns over declare/define. They
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// demonstrate that a programmatically-built enum carries a full enum through
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// codegen: `RecvResult(i64)` constructs and matches like any hand-written enum,
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// and is one nominal type across sites (the type-fn identity path). The channel
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// library (N3) consumes these once it lands.
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// A blocking recv: a value, or the channel was closed (drained).
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RecvResult :: ($T: Type) -> Type {
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return define(declare("RecvResult"), .enum(.{ variants = .[
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EnumVariant.{ name = "value", payload = T },
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EnumVariant.{ name = "closed", payload = void },
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] }));
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}
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// A non-blocking try-recv: a value, currently empty, or closed — three states
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// a bool can't express.
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TryResult :: ($T: Type) -> Type {
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return define(declare("TryResult"), .enum(.{ variants = .[
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EnumVariant.{ name = "value", payload = T },
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EnumVariant.{ name = "empty", payload = void },
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EnumVariant.{ name = "closed", payload = void },
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] }));
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}
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