In FunC (and in Tolk before), the assignment
> lhs = rhs
evaluation order (at IR level) was "rhs first, lhs second".
In practice, this did not matter, because lhs could only
be a primitive:
> (v1, v2) = getValue()
Left side of assignment actually has no "evaluation".
Since Tolk implemented indexed access, there could be
> getTensor().0 = getValue()
or (in the future)
> getObject().field = getValue()
where evaluation order becomes significant.
Now evaluation order will be to "lhs first, rhs second"
(more expected from user's point of view), which will become
significant when building control flow graph.
They are not keywords anymore.
> var cell = ...;
> var cell: cell = ...;
Motivation: in the future, when structures are implemented, this obviously should be valid:
> struct a { ... }
> var a = ...;
Struct fields will also be allowed to have names int/slice/cell.
FunC's (and Tolk's before this PR) type system is based on Hindley-Milner.
This is a common approach for functional languages, where
types are inferred from usage through unification.
As a result, type declarations are not necessary:
() f(a,b) { return a+b; } // a and b now int, since `+` (int, int)
While this approach works for now, problems arise with the introduction
of new types like bool, where `!x` must handle both int and bool.
It will also become incompatible with int32 and other strict integers.
This will clash with structure methods, struggle with proper generics,
and become entirely impractical for union types.
This PR completely rewrites the type system targeting the future.
1) type of any expression is inferred and never changed
2) this is available because dependent expressions already inferred
3) forall completely removed, generic functions introduced
(they work like template functions actually, instantiated while inferring)
4) instantiation `<...>` syntax, example: `t.tupleAt<int>(0)`
5) `as` keyword, for example `t.tupleAt(0) as int`
6) methods binding is done along with type inferring, not before
("before", as worked previously, was always a wrong approach)
