Thanks, I interpret layout as you say, but with the aim of preserving valid spacing if syntax elements are moved around as a result of AST modifications. My implementation flags those points, such as the contents of a let .. in, or a do expression.

In terms of ghc-exactprint, I actually think the technique I am using of converting all the original absolute locations to relative ones, editing the AST and then outputting it should be transferrable to haskell-src-exts too.

Alan

On Tue, Mar 10, 2015 at 8:05 PM, Andrew Gibiansky <andrew.gibiansky@gmail.com> wrote:
Just to be clear, I *think* layout rules don't apply here at all, actually. 

If I understand correctly, "layout" has to do with turning spacing into braces and semicolons. A new line is a semicolon. A brace group is inserted around things that are aligned where a brace group actually makes sense.

e.g. 

let x = y
    y = z 
  in ...

gets turned into roughly

let { x = y
    ; y = z
    } in ...

if-then-else however is just an expression, like a ternary operator, so it doesn't need any semicolons or braces. So layout is unrelated, except for the issue of `do` blocks inserting semicolons into `if-then-else` groups (and that's what DoAndIfThenElse fixes).

-- Andrew

PS. I am very glad someone is working on ghc-exactprint. It's a really important step in developing better Haskell tooling, imho. Doing that sort of thing right now with haskell-src-exts right now is a real pain (see half of the closed issues on hindent... about how it doesn't preserve formatting in many places.)

On Tue, Mar 10, 2015 at 9:25 AM, Alan & Kim Zimmerman <alan.zimm@gmail.com> wrote:
Ok, adding a do does make a difference. More complexity.

Thanks
  Alan

On Tue, Mar 10, 2015 at 6:06 PM, Brandon Allbery <allbery.b@gmail.com> wrote:
On Tue, Mar 10, 2015 at 12:01 PM, Alan & Kim Zimmerman <alan.zimm@gmail.com> wrote:
I am working on ghc-exactprint, and need to flag points where layout must be preserved, and considering the `if` statement.

My understanding of the layout rules for if then else is that the `then` has to start more to the right than the `if`.

I believe you are looking for DoAndIfThenElse.

--
brandon s allbery kf8nh                               sine nomine associates
allbery.b@gmail.com                                  ballbery@sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net


_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe