bux-lang/docs/ROADMAP.md

Bux Language Roadmap — New Constructs

Updated: 2026-06-08 | Status: In Progress

This document tracks planned language constructs beyond Phase 8 strategy.

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P0 — Critical (Unlocks Major Use Cases)

1. defer Statement

Why: No GC + no destructors = manual Free everywhere. defer is the pragmatic fix.

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
}

Implementation Steps:

1. Add tkDefer token (or reuse tkDefer if exists)
2. Add DeferStmt AST node (child: *Stmt)
3. Parser: parse defer <expr>; or defer { <block> }
4. C backend: collect all defers per block, emit cleanup code before every exit point (return, break, continue)
5. Handle LIFO ordering for multiple defers in same scope

Complexity: Low — localized to parser + C backend. No type system changes.

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2. Closures / Anonymous Functions

Why: Callbacks, iterators, functional APIs. Currently only named functions exist.

Syntax:

let add: func(int, int) -> int = |a, b| { return a + b; };
let nums: Array<int> = Array_New<int>();
Array_Filter(nums, |x| { return x > 10; });

Implementation Steps:

1. New AST node: ClosureExpr with params, body, captures
2. Parser: parse |param1, param2| -> Type { body }
3. Type system: closure type as func(Args) -> Ret + implicit capture struct
4. C backend: generate struct with captured vars + function pointer
5. Lifetime: ensure captures outlive closure usage

Complexity: High — touches parser, sema, type system, C backend.

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3. 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. Desugar to while loop using Iter_HasNext / Iter_Next or trait-based iterator
3. C backend: generate standard while loop with iterator state

Complexity: Medium — needs either trait system enhancement or hardcoded desugaring.

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P1 — High Impact

4. Operator Overloading

Why: Can't write arr[i], a + b, s1 == s2 for user types.

Syntax:

extend Array<T> {
    func operator[](self: Array<T>, idx: uint) -> T { ... }
    func operator+(self: Array<T>, other: Array<T>) -> Array<T> { ... }
}

Implementation Steps:

1. Parser: allow operator[], operator+, etc. as function names
2. Sema: resolve operator calls to user-defined functions when available
3. C backend: emit regular function call

Complexity: Medium — mainly sema + parser changes.

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5. Destructors / Drop Trait

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

Syntax:

extend Array<T> {
    func Drop(self: own Array<T>) {
        Array_Free(self);
    }
}

Implementation Steps:

1. Define Drop interface in stdlib
2. C backend: emit Drop(value) before variable goes out of scope
3. Respect move semantics — don't drop moved values

Complexity: High — needs ownership tracking + move semantics.

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6. String Interpolation

Why: Fmt_Fmt1("hello {0}", name) is verbose.

Syntax:

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

Implementation Steps:

1. Lexer: detect { inside string literals, parse interpolation expressions
2. Parser: create string concatenation AST node
3. Desugar to String_Concat calls or Fmt_FmtN

Complexity: Low — lexer/parser changes only.

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P2 — Nice to Have

7. Native switch / case

Why: match is powerful but overkill for simple integer dispatch. Jump tables are faster.

Syntax:

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

Implementation Steps:

1. Parser: switch expr { case literal: stmts ... default: stmts }
2. C backend: emit switch(expr) { case N: ... }

Complexity: Low — straightforward C mapping.

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8. Named / Default Parameters

Why: API ergonomics.

Syntax:

func HttpResponse(code: int = 200, contentType: String = "text/plain", body: String = "") -> Response { ... }
let r: Response = HttpResponse(body: "hello");  // code=200, contentType=default

Implementation Steps:

1. Parser: allow param: Type = defaultExpr
2. Sema: fill missing args at call sites
3. C backend: emit args in correct order with defaults

Complexity: Medium — sema changes for call resolution.

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Recommended Order

1. defer — Low complexity, huge impact, unlocks safe resource management immediately.
2. String interpolation — Low complexity, big ergonomics win.
3. switch/case — Low complexity, complements match for numeric dispatch.
4. Named/default parameters — Medium complexity, improves stdlib APIs.
5. Operator overloading — Medium complexity, transforms stdlib ergonomics.
6. Closures — High complexity, unlocks iterators and functional style.
7. for x in collection — Depends on closures or trait system.
8. Destructors / Drop — High complexity, needs ownership + move semantics.