bux-lang/docs/ROADMAP.md

Bux Language Roadmap — New Constructs

Updated: 2026-06-09 | Status: In Progress

This document tracks planned language constructs beyond Phase 8 strategy.

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✅ Done

1. defer Statement

Status: ✅ Implemented in both bootstrap and selfhost.

Syntax:

func ReadFile(path: String) -> String {
    let fd: int = Open(path);
    defer Close(fd);           // runs on any exit from scope
    defer PrintLine("done");   // LIFO order
    let data: String = ReadAll(fd);
    return data;               // both defers run before return
}

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2. Native switch / case

Status: ✅ Implemented in both bootstrap and selfhost. Desugars to if-else chain.

Syntax:

switch statusCode {
    case 200: PrintLine("OK");
    case 404: PrintLine("Not Found");
    case 500: PrintLine("Server Error");
    default:  PrintLine("Unknown");
}

---

3. Operator Overloading

Status: ✅ Implemented in bootstrap. Selfhost has no method-table yet (not needed for selfhost-loop parity).

Supported operators:

func Vec2_operator_add(self: *Vec2, other: Vec2) -> Vec2 { ... }
func Vec2_operator_sub(self: *Vec2, other: Vec2) -> Vec2 { ... }
func Vec2_operator_eq(self: *Vec2, other: Vec2) -> bool { ... }
func Vec2_operator_lt(self: *Vec2, other: Vec2) -> bool { ... }
func MyArray_operator_index_get(self: *MyArray, idx: int) -> int { ... }
func MyArray_operator_index_set(self: *MyArray, idx: int, value: int) { ... }

Notes:

• Works via method-table lookup in sema + hir_lower.
• Generic method instantiation supported.
• Short-circuit operators (&&, ||) remain builtin.

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4. String Interpolation

Status: ✅ Implemented in bootstrap (selfhost reserves AST node).

Syntax:

let name: String = "Bux";
let msg: String = f"Hello, {name}!";
let num: int = 42;
let msg2: String = f"Count: {num}";

Notes:

• f"..." prefix enables interpolation.
• Escaped braces: \{ and \}.
• Auto-converts int, uint, float, bool, and String inside braces.

---

5. Named / Default Parameters

Status: ✅ Implemented in both bootstrap and selfhost.

Syntax:

func HttpResponse(code: int = 200, body: String = "") -> Response { ... }
let r: Response = HttpResponse(body: "hello");  // code=200
let s = HttpResponse(404, body: "err");         // positional + named mixed

Notes:

• Bootstrap parser already parsed defaults; added named-arg parsing and sema injection.
• Selfhost parser parses = defaultExpr in params and name: value at call sites.
• Sema injects default expressions and reorders named args into param order.

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6. CLI Commands (bux new, bux init, bux test, bux fmt)

Status: ✅ Implemented in selfhost.

Command	Description
bux new <name>	Create a new project directory with bux.toml and src/Main.bux
bux init	Initialize a Bux project in the current directory
bux test [dir]	Build and run the project binary, reporting pass/fail
`bux fmt <file	dir>`

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7. Basic Borrow Checker (@[Checked])

Status: ✅ Implemented in selfhost.

Features:

• @[Checked] attribute enables per-function borrow checking.
• &T (shared reference) and &mut T (mutable reference) type syntax.
• Rejects write-through raw pointer (*T) in checked functions.
• Detects double mutable borrow (Swap(&mut x, &mut x)).
• Tracks use-after-move for own T values.

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P0 — Critical (Unlocks Major Use Cases)

8. Full Selfhost Bootstrap Loop

Why: The selfhost compiler must compile itself deterministically.

Status: ✅ Done — selfhost-loop produces identical C output on every iteration.

---

6. Closures / Anonymous Functions

Status: ✅ Implemented in both bootstrap and selfhost. Capture-less and with captures.

Syntax:

// Capture-less closure
let add: func(int, int) -> int = |a, b| { return a + b; };

// Closure with captures
let base: int = 10;
let adder: func(int) -> int = |a: int| -> int { return a + base; };
let result: int = adder(5);  // 15

// Pass closure to higher-order function
Array_Filter(nums, |x| { return x > 10; });

Implementation:

• Capture-less closures: generate global thunk function, return &thunk as function pointer.
• Closures with captures:
  1. Sema: Scope_LookupUpTo identifies captured variables from outer scope.
  2. HIR Lower: generate __closure_env_N struct + global instance __closure_env_instance_N.
  3. At closure creation site: emit capture assignments (env_instance.x = x;).
  4. In thunk body: rewrite captured identifiers to env_instance.x via hFieldAccess.
  5. C backend: emit env struct definition + global instance before thunk function.

Limitations: One global instance per closure AST node (no multiple instances). No loop/return support in closures yet.

Complexity: High — touches parser, sema, type system, HIR/LIR backend.

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7. for x in collection Iterator Loops

Why: Currently only for i in 0..10 works. No way to iterate arrays/channels/maps.

Syntax:

for item in arr {
    PrintLine(item);
}
for msg in channel {
    Process(msg);
}

Implementation Steps:

1. ✅ Parser: extend for to accept for <ident> in <expr> { ... }
2. ✅ Range-based: for i in lo..hi and for i in lo..=hi — desugared to while loop with counter
3. ✅ Collection-based: for x in arr — desugared to Array_Iter_T + Iter_HasNext_T + Iter_Next_T

Complexity: Medium — done.

---

P1 — High Impact

8. Destructors / Drop Trait

Status: ✅ Done in selfhost.

Why: own T exists but nothing cleans up automatically. Complements defer.

Syntax:

import Drop

struct Buffer {
    ptr: *int
}

extend Buffer for Drop {
    func Drop(self: *Buffer) {
        bux_free(self.ptr as *void);
    }
}

Implementation Steps:

1. ✅ Define Drop interface in stdlib (lib/Drop.bux)
2. ✅ HIR lowering: emit TypeName_Drop(&value) before variable goes out of scope (selfhost)
3. ✅ Respect move semantics — moved values are skipped via CBE_IsMoved

Notes:

• Bootstrap compiler still requires explicit defer for user-defined cleanup.
• See docs/superpowers/specs/2026-06-14-drop-interface-auto-drop-design.md.

Complexity: Medium — reused existing @[Drop] auto-drop path and interface method table.

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9. Trait Bounds (T: Comparable)

Why: Generic functions need constraints on type parameters.

Syntax:

func Sort<T: Comparable>(arr: &mut Array<T>) { ... }

Status: ✅ Implemented — @[Comparable] attribute + Sema_CheckTraitBounds in selfhost.

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10. CTFE (Compile-Time Function Execution)

Why: Precomputed tables for embedded / kernel dev.

Syntax:

const A: int = 10;
const B: int = 20;
const C: int = A + B;  // Evaluated at compile time

Status: ✅ Implemented — multi-pass expression evaluator in HIR lowering.

Supported: literals, binary/unary/ternary ops, casts, cross-const references.

---

P2 — Nice to Have

11. Concurrency

Why: Go-style goroutines + channels, but without GC.

Syntax:

let (tx, rx) = Channel::New<int>();
Task::Spawn(Worker, rx);

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Recommended Order

1. ✅ defer — Done
2. ✅ switch/case — Done
3. ✅ Operator overloading — Done (bootstrap)
4. ✅ String interpolation — Done (bootstrap)
5. ✅ Named/default parameters — Done
6. ✅ Basic borrow checker (@[Checked]) — Done (selfhost)
7. ✅ bux fmt, bux test, bux new, bux init — Done (selfhost)
8. ✅ Closures (capture-less) — Done
9. ✅ Closures with captures — Done
10. ✅ for x in collection — Done
11. ✅ Trait bounds (T: Comparable) — Done
12. ✅ CTFE — Done
13. ✅ Selfhost bootstrap loop — Done
14. ✅ Destructors / Drop — Done in selfhost.
15. Bounds checking on slices — Add Slice<T> type with bounds-checked indexing.
16. Concurrency — Green threads + channels.