Added else child to the if statement.

[Teemperor]

Without an else branch we would need a temp local for writing normal if/else statements. If someone just wants an normal if statement he/she can just use a empty block as an else.

Other suggestion if changing if is not up to debate: Add an ifelse and keep if the way it is.

[kg]

This is already the case for ml-proto, so lgtm.

[rossberg]

Actually, ml-proto allows else-less if (and treats it as else nop).

[jfbastien]

Children?

[Teemperor]

Thanks JF, fixed the spelling!

[jfbastien]

Is this mandating that both be present? Or is "else" optional?
Or should we have "ifelse" and "ifthenelse"?
@sunfishcode?

[Teemperor]

IMHO: The problem with an optional else branch is that it's weird to encode in the binary format (in a sexpr it is no problem obviously). An ifthen and ifthenelse could be shorter in binary (even though I have no idea about the planned compression which has a big influence on that).

[rossberg]

I'm not sure I understand the issue. This seems to be a concern about the binary format, not the AST semantics itself.

[Teemperor]

The current AST encoding is to my knowledge something like opcode {opcode data} {child-node} and ifthen/ifthenelse would save us many nop child nodes in the else child.

So instead of if-opcode condition then-node **nop** for a simple if, one could use ifthen-opcode condition then-node and save the byte for the nop opcode.

I know the discussion is not about the binary format, but the preliminary format would suffer from that issue (and I assume it will not change that much).

[kg]

(if (...) (nop)) and (if (nop) (...)) aren't especially difficult to encode, will stream compress okay, and shouldn't amount to that much of an executable's size. It's not really worth worrying about it at this stage, I think. We can introduce specialized if opcodes later.

Or we could introduce them now as syntax sugar, I guess, and reserve the right to turn them into actual opcodes if we need to.

[lukewagner]

lgtm to land as is and we can refine layer as we get serious about the binary encoding.

[sunfishcode]

With #427 merged, there are now separate if and if_else operators.