Convert FunC contracts to Tolk with a single command

Tolk is a new language for writing smart contracts in TON. Think of Tolk as the "next‑generation FunC". Tolk compiler is literally a fork of FunC compiler, introducing familiar syntax similar to TypeScript, but leaving all low-level optimizations untouched.

Using just one-line command, you can take your existing FunC file and immediately transform it to Tolk:

npx @ton/convert-func-to-tolk jetton-minter.fc

Example input: jetton-minter.fc
Example output: jetton-minter.tolk

Of course, the result will require some manual fixes, but definitely, almost all boilerplate is done automatically.

Installation

Not required: just use npx above.

Command-line options

npx above uses default options, but here is what you can pass:

• --warnings-as-comments — insert /* _WARNING_ */ comments (not just print warnings to output)
• --no-camel-case — don't transform snake_case to camelCase

What exactly this converter does

• Converts ;; comment → // comment
• Converts #include → import
• Removes deprecated #pragma
• Changes function syntax: int f(slice a) → fun f(a: slice): int
• Changes globals declarations: global slice cs → global cs: slice
• Changes variable declarations: int a = 0 → var a: int = 0
• Changes complex variable declarations: var (int a, slice b) = … → var (a: int, b: slice) = …
• Removes impure specifiers (inserting @pure for asm functions)
• Replaces inline and inline_ref specifiers with @ attributes
• Converts method_id to get methods: int seqno() method_id → get seqno(): int
• Converts forall to generics syntax: forall X -> X f() → fun f<X>(): X
• Removes forward declarations, since Tolk locates symbols in advance, like most languages
• Wraps invalid identifiers into backticks: op::increase → `op::increase`
• Replaces ifnot (x) → if (!x) and similar
• Replaces throw_unless(condition, excNo) → assert(excNo, condition) and similar
• Replaces null() → null
• Replaces null?(x) → x == null
• Does all stdlib renaming: begin_cell → beginCell, endParse → assertEndOfSlice, etc.
• Converts ~ declarations: (slice, int) ~load_op(slice s) { return s~load_uint(32); } → fun loadOp(mutate self: slice): int { return self.loadUint(32); }
• Replaces ~method() with .method()
• Replaces entrypoints: recv_internal → onInternalMessage and similar
• Converts functions and locals from snake_case to camelCase (globals/constants no, since a converter works per-file, whereas they are often imported)
• ... and lots of other stuff, actually

Of course, the convertion result can seem quite dirty. For instance, Tolk has logical operators, and therefore if (~ found) could probably be if (!found). For instance, flags & 1 could probably be isMessageBounced(flags). For instance, assert(!(a < 0)) is actually assert(a >= 0). For instance, const `op::increase` would better be const OP_INCREASE. And so on.

Contracts written in Tolk from scratch would definitely look nicer. But that's what exactly expected from auto-conversion.

Typical problems in Tolk code after conversion

Almost all problems are related to mutable methods. If FunC had ~methods and .methods, Tolk has only .methods, which may mutate, or may not, the first self parameter. Hence, if a method was called in a strange way in FunC, it becomes an incorrect call in Tolk:

// FunC
int r = n~divmod(10);
// auto-converted, incorrect now
var r: int = n.divMod(10);

Obviously, this line should be rewritten:

var (newN, r) = divMod(n, 10);
// use newN or assign n = newN
// alternatively, use `redef` keyword:
var (n redef, r) = divMod(n, 10);

Lots of stdlib functions became mutating. This way, cs~load_int(32) replaced by cs.loadInt(32) works equally, but cs.skip_bits(8) (with dot! not tilda) replaced by cs.skipBits(8) works differently, because skipBits() mutates an object.

Hence, if you used dot-call for .methods which become mutating, that part should be rewritten (it either won't compile or would work differently). Most common cases are skip-functions and dict-functions. Dict API in Tolk is mutating. If you used dict~udict_set(…), it was replaced by dict.uDictSet(…), and everything is fine. But if you used dict.udict_set(…) to obtain a copy, it's a problem.

The converter prints warnings in such cases. Some are falsy, but most are related to this exact problem.

Besides mutability, some stdlib functions were removed. For instance, pair(a,b) removed, as it can be replaced with [a,b]. As well as various functions working with tuples, which are supposed to be expressed syntactically.

Statistically, mutability covers about 90% of manual post-fixes, removed functions about 5%, and the rest 5% are minors.

Remember, that contracts written in Tolk from scratch would definitely look nicer than being auto-converted. For instance, using logical operators instead of bitwise tremendously increases code readability.