RFC: Compiler improvements

[nbd168]

Bring ucode closer to ECMAScript:

1. allow export function without trailing semicolon
2. add explicit function declaration syntax

[jow-]

Export without trailing semicolon is fine, makes sense.

About the hoisting support; personally I am no fan of hoisting at all, it is confusing and counterintuitive and, as you've noticed with the compiler implementation, makes single-pass compilation impossible and requires juggling and swapping states.

I do agree that function hoisting for enabling mutual recursion is fine but things like

let x = foo();

function foo() {

}

Just do not feel right (yes I know it is established practise in JS / ECMA Script).
What I was considering the past is simple function forward declarations:

function foo;
let x = foo();

function foo() {

}

function is_odd;
function is_even(n) { return n == 0 ? true : is_odd(n - 1); }
function is_odd(n) { return n == 0 ? false : is_even(n - 1); }

print(is_even(4), "\n");
print(is_odd(3), "\n");

It is slightly more verbose but simplifies compiler implementation a lot and clearly communicates intent.

[nbd168]

Fair enough. So function foo; as an alternative for the currently used let foo; variant except with enforced function type, right? I can look into that.

[jow-]

Yes, a not fully fleshed out proposal is:

• function foo; reserves a slot and constrains foo to function type
• treat as constant: function foo; foo = function() {} -> Syntax error: Invalid assignment to constant 'foo'
• attempts to redeclare foo result in a syntax error: function foo; let foo = 1; => Syntax error: Function 'foo' redeclared as different kind of symbol or Syntax error: Function 'foo' redeclared
• a function stub (forward declaration) might only be declared once:
  • function foo; function foo() {} -> okay
  • function foo; function foo() {}; function foo() {} -> Syntax error: Function 'foo' redeclared
• multiple forward declarations: undecided. If we treat it like let and const, it would be disallowed (let x; let x; -> Syntax error: Variable 'x' redeclared), but given that function prototypes have special semantics it might make sense to allow multiple ones (function foo; function foo; function foo() {}), to also mimic the behavior of C somewhat
• forward declaration after actual declaration: depends on what is decided for the previous point. Gut feeling would be to disallow (function foo() {}; function foo; -> Syntax error: Function 'foo' redeclared) but it would probably negatively impact the usefulness of forward declarations as "safe way" to mark an identifer as callable value implemented somewhere
• Call on forward declaration never fully declared -> runtime error Type error: left-hand side is not a function like let foo; foo();

[nbd168]

Does this look like what you wanted?

[jow-]

Yes! I hope to merge it during the weekend, on a first glance it looks really good.