Wrong let expression parsing

[auduchinok]

The contents of do in the following code should be parsed as a sequence of let expression and x, but it's parsed as let expression in sequence of the sum and x.

do
 let x = 1 in x + 1
 x

In addition to the unexpected tree form it also creates a wrong scope for x.

AST viewer

[abelbraaksma]

Wait, doesn't in introduce scope? Shouldn't the last line x be out of scope for x?

(I admit I'm not sure of this, I use the in syntax rarely)

[auduchinok]

@abelbraaksma It does, and its scope should be x + 1 here.

[abelbraaksma]

Edit, I may misunderstand the scoping here, as this seems to work properly well, it works, not sure of "properly":

let _ =
 let x = 1 in x + 2
 x // in scope?

And if I take your code and paste it in VS, it correctly seems to say for each line that you're returning a value when you should return unit. But it appears to get the line number wrong for the second error.

If I remove the in it still gets the line number wrong (maybe not related to this issue):

[auduchinok]

I'd expect it to be parsed as:

do
 (let x = 1 in (x + 1));
 x

And the latter x would be unresolved.

[dsyme]

This is a long-standing issue and I think there are various duplicates of it. I suspect the right approach here is to start raising warnings when this formulation is used

[auduchinok]

@dsyme How bad would be changing the parsing rules here?