Tolk vs FunC: in detail

A very huge list below. Will anyone have enough patience to read it up to the end?..

There is a compact version

✅ Traditional comments :)

FunC	Tolk
`;; comment`	`// comment`
`{- multiline comment -}`	`/* multiline comment */`

✅ `2+2` is 4, not an identifier. Identifiers can only be alpha-numeric

In FunC, almost any character can be a part of identifier. For example, 2+2 (without a space) is an identifier. You can even declare a variable with such a name.

In Tolk, spaces are not mandatory. 2+2 is 4, as expected. 3+~x is 3 + (~ x), and so on.

FunC	Tolk
return 2+2; ;; undefined function `2+2`	`return 2+2; // 4`

More precisely, an identifier can start from [a-zA-Z$_] and be continued with [a-zA-Z0-9$_]. Note, that ?, :, and others are not valid symbols, found? and op::increase are not valid identifiers.

You can use backticks to surround an identifier, and then it can contain any symbols (similar to Kotlin and some other langs). Its potential usage is to allow keywords be used as identifiers, in case of code generation by a scheme, for example.

FunC	Tolk
`const op::increase = 0x1234;`	`const OP_INCREASE = 0x1234;`
`;; even 2%&!2 is valid int 2+2 = 5;`	// don't do like this :) var `2+2` = 5;

✅ Impure by default, compiler won't drop user function calls

FunC has an impure function specifier. When absent, a function is treated as pure. If its result is unused, its call was deleted by the compiler.

Though this behavior is documented, it is very unexpected to newcomers. For instance, various functions that don't return anything (throw an exception on mismatch, for example), are silently deleted. This situation is spoilt by the fact that FunC doesn't check and validate function body, allowing impure operations inside pure functions.

In Tolk, all functions are impure by default. You can mark a function pure with annotation, and then impure operations are forbidden in its body (exceptions, globals modification, calling non-pure functions, etc.).

✅ New functions syntax: `fun` keyword, `@` attributes, types on the right (like in TypeScript, Kotlin, Python, etc.)

FunC	Tolk
`cell parse_data(slice cs) { }`	`fun parse_data(cs: slice): cell { }`
`(cell, int) load_storage() { }`	`fun load_storage(): (cell, int) { }`
`() main() { ... }`	`fun main() { ... }`

Types of variables — also to the right:

FunC	Tolk
`slice cs = ...;`	`var cs: slice = ...;`
`(cell c, int n) = parse_data(cs);`	`var (c: cell, n: int) = parse_data(cs);`
`global int stake_at;`	`global stake_at: int;`

Modifiers inline and others — with annotations:

FunC	Tolk
`int f(cell s) inline {`	`@inline fun f(s: cell): int {`
`() load_data() impure inline_ref {`	`@inline_ref fun load_data() {`
`global int stake_at;`	`global stake_at: int;`

forall — this way:

FunC	Tolk
`forall X -> tuple cons(X head, tuple tail)`	`fun cons<X>(head: X, tail: tuple): tuple`

asm implementation — like in FunC, but being properly aligned, it looks nicer:

@pure
fun third<X>(t: tuple): X
    asm "THIRD";

@pure
fun iDictDeleteGet(dict: cell, keyLen: int, index: int): (cell, slice, int)
    asm(index dict keyLen) "DICTIDELGET NULLSWAPIFNOT";

@pure
fun mulDivFloor(x: int, y: int, z: int): int
    builtin;

There is also a @deprecated attribute, not affecting compilation, but for a human and IDE.

✅ `get` instead of `method_id`

In FunC, method_id (without arguments) actually declared a get method. In Tolk, you use a straightforward syntax:

FunC	Tolk
`int seqno() method_id { ... }`	`get seqno(): int { ... }`

Both get methodName() and get fun methodName() are acceptable.

For method_id(xxx) (uncommon in practice, but valid), there is an attribute:

FunC	Tolk
`() after_code_upgrade(cont old_code) impure method_id(1666)`	`@method_id(1666) fun afterCodeUpgrade(oldCode: continuation)`

✅ It's essential to declare types of parameters (though optional for locals)

// not allowed
fun do_smth(c, n)
// types are mandatory
fun do_smth(c: cell, n: int)

If parameter types are mandatory, return type is not (it's often obvious of verbose). If omitted, it's auto inferred:

fun x() { ... }  // auto infer from return statements

For local variables, types are also optional:

var i = 10;                      // ok, int
var b = beginCell();             // ok, builder
var (i, b) = (10, beginCell());  // ok, two variables, int and builder

// types can be specified manually, of course:
var b: builder = beginCell();
var (i: int, b: builder) = (10, beginCell());

✅ Variables are not allowed to be redeclared in the same scope

var a = 10;
...
var a = 20;  // error, correct is just `a = 20`
if (1) {
    var a = 30;  // it's okay, it's another scope
}

As a consequence, partial reassignment is not allowed:

var a = 10;
...
var (a, b) = (20, 30);  // error, releclaration of a

Note, that it's not a problem for loadUint() and other methods. In FunC, they returned a modified object, so a pattern var (cs, int value) = cs.load_int(32) was quite common. In Tolk, such methods mutate an object: var value = cs.loadInt(32), so redeclaration is unlikely to be needed.

fun send(msg: cell) {
    var msg = ...;  // error, redeclaration of msg

    // solution 1: intruduce a new variable
    var msgWrapped = ...;
    // solution 2: use `redef`, though not recommended
    var msg redef = ...;

✅ Changes in the type system

FunC's type system is based on Hindley-Milner. This is a common approach for functional languages, where types are inferred from usage through unification.

In Tolk v0.7, the type system is rewritten from scratch. In order to add booleans, fixed-width integers, nullability, structures, and generics, we must have a static type system (like TypeScript or Rust). Because Hindley-Milner will clash with structure methods, struggle with proper generics, and become entirely impractical for union types (despite claims that it was "designed for union types").

We have the following types:

int, bool, cell, slice, builder, untyped tuple
typed tuple [T1, T2, ...]
tensor (T1, T2, ...)
callables fun(TArgs) -> TResult
void (more canonical to be named unit, but void is more reliable)
self, to make chainable methods, described below; actually it's not a type, it can only occur instead of return type of a function

The type system obeys the following rules:

variable types can be specified manually or are inferred from declarations, and never change after being declared
function parameters must be strictly typed
function return types, if unspecified, inferred from return statements similar to TypeScript; in case of recursion (direct or indirect), the return type must be explicitly declared somewhere
generic functions are supported

✅ Clear and readable error messages on type mismatch

In FunC, due to Hindley-Milner, type mismatch errors are very hard to understand:

error: previous function return type (int, int)
cannot be unified with implicit end-of-block return type (int, ()):
cannot unify type () with int

In Tolk, they are human-readable:

1) can not assign `(int, slice)` to variable of type `(int, int)`
2) can not call method for `builder` with object of type `int`
3) can not use `builder` as a boolean condition
4) missing `return`
...

✅ `bool` type, casting `boolVar as int`

Under the hood, bool is still -1 and 0 at TVM level, but from the type system's perspective, bool and int are now different.

Comparison operators == / >= /... return bool. Logical operators && || return bool. Constants true and false have the bool type. Lots of stdlib functions now return bool, not int (having -1 and 0 at runtime):

var valid = isSignatureValid(...);    // bool
var end = cs.isEndOfSlice();          // bool

Operator !x supports both int and bool. Condition of if and similar accepts both int (!= 0) and bool. Logical && and || accept both bool and int, preserving compatibility with constructs like a && b where a and b are integers (!= 0).

Arithmetic operators are restricted to integers, only bitwise and logical allowed for bools:

valid && end;    // ok
valid & end;     // ok, bitwise & | ^ also work if both are bools
if (!end)        // ok

if (~end)        // error, use !end
valid + end;     // error
8 & valid;       // error, int & bool not allowed

Note, that logical operators && || (missed in FunC) use IF/ELSE asm representation always. In the future, for optimization, they could be automatically replaced by & | when it's safe (example: a > 0 && a < 10). To manually optimize gas consumption, you can still use & | (allowed for bools), but remember, that they are not short-circuit.

bool can be cast to int via as operator:

var i = boolValue as int;  // -1 / 0

There are no runtime transformations. bool is guaranteed to be -1/0 at TVM level, so this is type-only casting. But generally, if you need such a cast, probably you're doing something wrong (unless you're doing a tricky bitwise optimization).

✅ Generic functions and instantiations like `f<int>(...)`

In FunC, there were "forall" functions:

forall X -> tuple tpush(tuple t, X value) asm "TPUSH";

Tolk introduces properly made generic functions. Their syntax reminds mainstream languages:

fun tuplePush<T>(mutate self: tuple, value: T): void
    asm "TPUSH";

When f<T> is called, T is detected (in most cases) by provided arguments:

t.tuplePush(1);     // detected T=int
t.tuplePush(cs);    // detected T=slice
t.tuplePush(null);  // error, need to specify "null of what type"

The syntax f<int>(...) is also supported:

t.tuplePush<int>(1);     // ok
t.tuplePush<int>(cs);    // error, can not pass slice to int
t.tuplePush<int>(null);  // ok, null is "null of type int"

User-defined functions may also be generic:

fun replaceLast<T>(mutate self: tuple, value: T) {
    val size = self.tupleSize();
    self.tupleSetAt(value, size - 1);
}

Having called replaceLast<int> and replaceList<slice> will result in TWO generated asm (fift) functions. Actually, they mostly remind "template" functions. At each unique invocation, function's body is fully cloned under a new name.

There may be multiple generic parameters:

fun replaceNulls<T1, T2>(tensor: (T1, T2), v1IfNull: T1, v2IfNull: T2): (T1, T2) {
    var (a, b) = tensor;
    return (a == null ? v1IfNull : a, b == null ? v2IfNull : b);
}

A generic parameter T may be something complex.

fun duplicate<T>(value: T): (T, T) {
    var copy: T = value;
    return (value, copy);
}

duplicate(1);         // duplicate<int>
duplicate([1, cs]);   // duplicate<[int, slice]>
duplicate((1, 2));    // duplicate<(int, int)>

Or even functions, it also works:

fun callAnyFn<TObj, TResult>(f: fun(TObj) -> TResult, arg: TObj) {
    return f(arg);
}

fun callAnyFn2<TObj, TCallback>(f: TCallback, arg: TObj) {
    return f(arg);
}

Note, that while generic T are mostly detected from arguments, there are not so obvious corner cases, when T does not depend from arguments:

fun tupleLast<T>(self: tuple): T
    asm "LAST";

var last = t.tupleLast();    // error, can not deduce T

To make this valid, T should be provided externally:

var last: int = t.tupleLast();       // ok, T=int
var last = t.tupleLast<int>();       // ok, T=int
var last = t.tupleLast() as int;     // ok, T=int

someF(t.tupleLast());       // ok, T=(paremeter's declared type)
return t.tupleLast();       // ok if function specifies return type

Also note, that T for asm functions must occupy 1 stack slot (otherwise, asm body is unable to handle it properly), whereas for a user-defined function, T could be of any shape.

In the future, when structures and generic structures are implemented, all the power of generic functions will come into play.

✅ Another naming for recv_internal / recv_external

fun onInternalMessage
fun onExternalMessage
fun onTickTock
fun onSplitPrepare
fun onSplitInstall

All parameter types and their order rename the same, only naming is changed. fun main is also available.

✅ #include → import. Strict imports

FunC	Tolk
`#include "another.fc";`	`import "another.tolk"`

In Tolk, you can not used a symbol from a.tolk without importing this file. In other words, "import what you use".

All stdlib functions are available out of the box, downloading stdlib and #include "stdlib.fc" is not needed. See below about embedded stdlib.

There is still a global scope of naming. If f is declared in two different files, it's an error. We "import" a whole file, no per-file visibility and export keyword is now supported, but probably will be in the future.

✅ #pragma → compiler options

In FunC, "experimental" features like allow-post-modifications were turned on by a pragma in .fc files (leading to problems when some files contain it, some don't). Indeed, it's not a pragma for a file, it's a compilation option.

In Tolk, all pragmas were removed. allow-post-modification and compute-asm-ltr were merged into Tolk sources (as if they were always on in FunC). Instead of pragmas, there is now an ability to pass experimental options.

As for now, there is one experimental option introduced — remove-unused-functions, which doesn't include unused symbols to Fift output.

#pragma version xxx was replaced by tolk xxx (no >=, just a strict version). It's good practice to annotate compiler version you are using. If it doesn't match, Tolk will show a warning.

tolk 0.6

✅ Late symbols resolving. AST representation

In FunC (like in С) you can not access a function declared below:

int b() { a(); }   ;; error
int a() { ... }    ;; since it's declared below

To avoid an error, a programmer should create a forward declaration at first. The reason is that symbols resolving is performed right at the time of parsing.

Tolk compiler separates these two steps. At first it does parsing, and then it does symbol resolving. Hence, a snippet above would not be erroneous.

Sounds simple, but internally, it's a very huge job. To make this available, I've introduced an intermediate AST representation, completely missed in FunC. That's an essential point of future modifications and performing semantic code analisys.

✅ `null` keyword

Creating null values and checking variables on null looks very pretty now.

FunC	Tolk
`a = null()`	`a = null`
`if (null?(a))`	`if (a == null)`
`if (~ null?(b))`	`if (b != null)`
`if (~ cell_null?(c))`	`if (c != null)`

Note, that it does NOT mean that Tolk language has nullability. No, you can still assign null to an integer variable — like in FunC, just syntactically pleasant. A true nullability will be available someday, after hard work on the type system.

✅ `throw` and `assert` keywords

Tolk greatly simplifies working with exceptions.

If FunC has throw(), throw_if(), throw_arg_if(), and the same for unless, Tolk has only two primitives: throw and assert.

FunC	Tolk
`throw(excNo)`	`throw excNo`
`throw_arg(arg, excNo)`	`throw (excNo, arg)`
`throw_unless(excNo, condition)`	`assert(condition, excNo)`
`throw_if(excNo, condition)`	`assert(!condition, excNo)`

Note, that !condition is possible since logical NOT is available, see below.

There is a long (verbose) syntax of assert(condition, excNo):

assert(condition) throw excNo;
// with possibility to include arg to throw

Also, Tolk swaps catch arguments: it's catch (excNo, arg), both optional (since arg is most likely empty).

FunC	Tolk
`try { } catch (_, _) { }`	`try { } catch { }`
`try { } catch (_, excNo) { }`	`try { } catch(excNo) { }`
`try { } catch (arg, excNo) { }`	`try { } catch(excNo, arg) { }`

✅ `do ... until` → `do ... while`

FunC	Tolk
`do { ... } until (~ condition);`	`do { ... } while (condition);`
`do { ... } until (condition);`	`do { ... } while (!condition);`

Note, that !condition is possible since logical NOT is available, see below.

✅ Operator precedence became identical to C++ / JavaScript

In FunC, such code if (slices_equal() & status == 1) is parsed as if( (slices_equal()&status) == 1 ). This is a reason of various errors in real-world contracts.

In Tolk, & has lower priority, identical to C++ and JavaScript.

Moreover, Tolk fires errors on potentially wrong operators usage to completely eliminate such errors:

if (flags & 0xFF != 0)

will lead to a compilation error (similar to gcc/clang):

& has lower precedence than ==, probably this code won't work as you expected.  Use parenthesis: either (... & ...) to evaluate it first, or (... == ...) to suppress this error.

Hence, the code should be rewritten:

// either to evaluate it first (our case)
if ((flags & 0xFF) != 0)
// or to emphasize the behavior (not our case here)
if (flags & (0xFF != 0))

I've also added a diagnostic for a common mistake in bitshift operators: a << 8 + 1 is equivalent to a << 9, probably unexpected.

int result = a << 8 + low_mask;

error: << has lower precedence than +, probably this code won't work as you expected.  Use parenthesis: either (... << ...) to evaluate it first, or (... + ...) to suppress this error.

Operators ~% ^% /% ~/= ^/= ~%= ^%= ~>>= ^>>= no longer exist.

✅ Immutable variables, declared via `val`

Like in Kotlin: var for mutable, val for immutable, optionally followed by a type. FunC has no analogue of val.

val flags = msgBody.loadMessageFlags();
flags &= 1;         // error, modifying an immutable variable

val cs: slice = c.beginParse();
cs.loadInt(32);     // error, since loadInt() mutates an object
cs.preloadInt(32);  // ok, it's a read-only method

Parameters of a function are mutable, but since they are copied by value, called arguments aren't changed. Exactly like in FunC, just to clarify.

fun some(x: int) {
    x += 1;
}

val origX = 0;
some(origX);      // origX remains 0

fun processOpIncrease(msgBody: slice) {
    val flags = msgBody.loadInt(32);
    ...
}

processOpIncrease(msgBody);  // by value, not modified

In Tolk, a function can declare mutate parameters. It's a generalization of FunC ~ tilda functions, read below.

✅ Deprecated command-line options removed

Command-line flags -A, -P, and others, were removed. Default behavior

/path/to/tolk {inputFile}

is more than enough. Use -v to print version and exit. Use -h for all available command-line flags.

Only one input file can be passed, others should be import'ed.

✅ stdlib functions renamed to verbose clear names, camelCase style

All naming in standard library was reconsidered. Now, functions are named using longer, but clear names.

FunC	Tolk
`cur_lt() car(l) get_balance().pair_first() raw_reserve(count) dict~idict_add?(...) dict~udict::delete_get_max() t~tpush(triple(x, y, z)) s.slice_bits() ~dump(x) ...`	`getLogicalTime() listGetHead(l) getMyOriginalBalance() reserveToncoinsOnBalance(count) dict.iDictSetIfNotExists(...) dict.uDictDeleteLastAndGet() t.tuplePush([x, y, z]) s.getRemainingBitsCount() debugPrint(x) ...`

A former "stdlib.fc" was split into multiple files: common.tolk, tvm-dicts.tolk, and others.

Continue here: Tolk vs FunC: standard library.

✅ stdlib is now embedded, not downloaded from GitHub

FunC	Tolk
Download stdlib.fc from GitHub Save into your project `#include "stdlib.fc";` Use standard functions	Use standard functions

In Tolk, stdlib a part of distribution. Standard library is inseparable, since keeping a triple "language, compiler, stdlib" together is the only correct way to maintain release cycle.

It works in such a way. Tolk compiler knows how to locate a standard library. If a user has installed an apt package, stdlib sources were also downloaded and exist on a hard disk, so the compiler locates them by system paths. If a user uses a WASM wrapper, they are provided by tolk-js. And so on.

Standard library is split into multiple files: common.tolk (most common functions), gas-payments.tolk (calculating gas fees), tvm-dicts.tolk, and others. Functions from common.tolk are available always (a compiler implicitly imports it). Other files are needed to be explicitly imported:

import "@stdlib/tvm-dicts"   // ".tolk" optional

...
var dict = createEmptyDict();
dict.iDictSet(...);

Mind the rule "import what you use", it's applied to @stdlib/... files also (with the only exception of "common.tolk").

JetBrains IDE plugin automatically discovers stdlib folder and inserts necessary imports as you type.

✅ Logical operators `&& ||`, logical not `!`

In FunC, there are only bitwise operators ~ & | ^. Developers making first steps, thinking "okay, no logical, I'll use bitwise in the same manner", often do errors, since operator behavior is completely different:

`a & b`	`a && b`
sometimes, identical:
`0 & X = 0`	`0 & X = 0`
`-1 & X = -1`	`-1 & X = -1`
but generally, not:
`1 & 2 = 0`	`1 && 2 = -1 (true)`

`~ found`	`!found`
sometimes, identical:
`true (-1) → false (0)`	`-1 → 0`
`false (0) → true (-1)`	`0 → -1`
but generally, not:
`1 → -2`	`1 → 0 (false)`

`condition & f()`	`condition && f()`
`f()` is called always	`f()` is called only if `condition`

`condition \| f()`	`condition \|\| f()`
`f()` is called always	`f()` is called only if `condition` is false

Tolk supports logical operators. They behave exactly as you get used to (right column). For now, && and || sometimes produce not optimal Fift code, but in the future, Tolk compiler will become smarter in this case. It's negligible, just use them like in other languages.

FunC	Tolk
`if (~ found?)`	`if (!found)`
`if (~ found?) { if (cs~load_int(32) == 0) { ... } }`	`if (!found && cs.loadInt(32) == 0) { ... }`
`ifnot (cell_null?(signatures))`	`if (signatures != null)`
`elseifnot (eq_checksum)`	`else if (!eqChecksum)`

Keywords ifnot and elseifnot were removed, since now we have logical not (for optimization, Tolk compiler generates IFNOTJMP, btw). Keyword elseif was replaced by traditional else if.

Remember, that a boolean true, transformed as int, is -1, not 1. It's a TVM representation.

✅ No tilda `~` methods, `mutate` keyword instead

This change is so huge that it's described on a separate page: Tolk mutability.

Tolk vs FunC gas consumption

TLDR

Tolk gas consumption could be a bit higher, because it fixes unexpected arguments shuffling in FunC. It's negligible in practice.
In the future, Tolk compiler will become smart enough to reorder arguments targeting less stack manipulations, but still avoiding a shuffling problem.

FunC compiler could unexpectedly shuffle arguments when calling an assembly function:

some_asm_function(f1(), f2());

Sometimes, f2() could be called before f1(), and it's unexpected. To fix this behavior, one could specify #pragma compute-asm-ltr, forcing arguments to be always evaluated in ltr-order. This was experimental, and therefore turned off by default.

This pragma reorders arguments on a stack, often leading to more stack manipulations than without it. In other words, in fixes unexpected behavior, but increases gas consumption.

Tolk puts arguments onto a stack exactly the same as if this pragma turned on. So, its gas consumption is sometimes higher than in FunC if you didn't use this pragma. Of course, there is no shuffling problem in Tolk.

In the future, Tolk compiler will become smart enough to reorder arguments targeting less stack manipulations, but still avoiding a shuffling problem.

✅ Traditional comments :)

✅ 2+2 is 4, not an identifier. Identifiers can only be alpha-numeric

✅ Impure by default, compiler won't drop user function calls

✅ New functions syntax: fun keyword, @ attributes, types on the right (like in TypeScript, Kotlin, Python, etc.)

✅ get instead of method_id