c.braced(node.exprs.map(ppAstAsmExpression))

Depending on the order PRs get merged, you might not have this problem here at all :)

Thanks, but I've already removed the asm expression lists from the grammar, such that { ... } are prohibited. At least until we may or may not make sense of them ourselves and without Fift's aid.

Didn't remove it there in pretty printer yet, but will.

Unfortunately all newline characters get parsed as spaces and are completely erased from AST. There is no way to pretty-print this at all.

I can imagine only one way to make this work without adding ; or some other explicit way to terminate lines: put this into a separate grammar with its own spaces rule.

Hmm, I'm thinking of the Prettier's approach with trying to fit as much as allowed in 80, 120 or other column limits, and put all excesses on new lines. Or, to simply put a newline character after each instruction — to keep all prior primitives required for it on the same line.

The second option sounds best from legibility perspective as well:

asm fun showcase(a: Int, b: Int, c: Int): Int {
    s0 s1 s2 XCHG3
    s1 s2 s0 XCHG3
    DROP2
}

Oh, and it would be nice to also check if the instructions are written on the same line with the opening and closing braces { ... }, i.e. when the start row of the function body equals its end row. Because if that's the case, we should respect the author's intent and inline everything there: add spaces after instructions, not newlines.