"Simon Peyton-Jones" <simonpj@microsoft.com> writes:

I didn't phrase it right. I meant that a let/lambda/if always extends to the next relevant (not part of a smaller expression) punctuation symbol; and if that phrase parses as an exp that's fine, otherwise it's a parse error. So I should not really speak in terms of 'ambiguity'.

Perhaps we can simply say that let .. in exp is legal only if the phrase is followed by one of the punctuation symbols. That's nice, because we don't need to talk of "not part of a smaller expression".

So (let x = 10 in x `div`) would be rejected because x `div` isn't a exp.

If you're going to modify the syntax in the report to match what implementors actually implement, you may also want to change the "illegal lexeme" definition for closing implicit layout. I believe that do a == b == c is (according to the Standard) legal syntax that means (do {a == b}) == c but I'll bet that most if not all Haskell parsers would get it wrong. Carl Witty