🫧 Tolk v1.2: rich bounced messages, cheap deployment, and a breaking change that you'll love

Tolk v1.2 is here, aligned with TVM 12 — bringing new assembler instructions that make contracts cheaper and cleaner.

This update introduces one breaking change, several powerful new capabilities, and a few quality-of-life improvements across the compiler.

✅ Notable changes in Tolk v1.2:

1. Breaking change: address is now "internal only"
2. Rich bounces: not 256 bits, but the full body on bounce
3. Cheap builder-to-slice, StateInit, and address composition
4. Improved compilation errors
5. Anonymous functions (lambdas)
6. Borrow checker to catch undefined behavior

PR on GitHub with detailed info.

✔ `address` is now "internal only"

Before:
* address meant internal/external/none

Now:
* address — internal only
* address? (nullable) — internal/none, exactly like "maybe address" in @ton/core
* any_address — internal/external/none

In 99% of contracts only internal addresses are used. External ones are rare, and "none" can be expressed as nullable.

struct Storage {

    // internal, checked automatically

    owner: address

}

With new TVM 12 instructions, addresses are validated automatically during (de)serialization without extra gas — no more manual isInternal() checks.

So yes, it's technically a breaking change, but it removes a ton of noise.

A short migration guide, as well as technical details, available here.

✔ Rich bounced messages

Historically, a bounced message only returned the first 256 bits of the original body.

Now TVM 12 supports rich bounces — which lets you obtain the entire body instead.

createMessage({

    bounce: BounceMode.RichBounce,

    ...

})

In onBouncedMessage, you get access to the original body, exit code, gas used, and more.

Old true/false bounce flags still work for backward compatibility.

Rich bounces simplify complex message flows and inter-contract communication — one of the most painful aspects of TON until now.

✔ Cheap builder-to-slice and address composition

Previously, converting a builder to a slice (endCell + beginParse) consumed a lot of gas because cells are expensive. Now there's a new instruction — BTOS (builder-to-slice) — without intermediate cell creation.

- b.endCell().beginParse() is now cheap: auto-optimized to BTOS
- "builder-to-address" is the same BTOS; hacks around "return a builder with a valid address" can be removed
- cheaper StateInit hashing and address calculations

Just update to Tolk v1.2 + TVM 12, and you'll immediately save gas.

✔ Anonymous functions (lambdas)

Can be used in general-purpose frameworks, perfectly integrated with the type system:

fun customRead(reader: (slice) -> int) { ... }



customRead(fun(s) {

    return s.loadUint(32)

})

✔ Low-level compiler enhancements

Also included: better diagnostics with precise ranges, new peephole optimizations, tuple ↔ object conversions, and multiple small fixes. A lightweight borrow checker prevents undefined behavior on concurrent mutations.

As always, all additions are carefully described in a PR.

🌳 We've also started improving TVM itself — new assembler instructions are designed specifically to fit the Tolk type system and optimizer. I have always said: the language is just the beginning. Perfect developer experience requires improving every layer of TON's stack. The road may be sharp and curvy — but we're definitely heading in the right direction.