Re: [Haskell-cafe] Layout rules for if then else

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

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wrote:

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Ok, adding a do does make a difference. More complexity.

Thanks Alan

On Tue, Mar 10, 2015 at 6:06 PM, Brandon Allbery wrote:

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On Tue, Mar 10, 2015 at 12:01 PM, Alan & Kim Zimmerman < alan.zimm@gmail.com> wrote:

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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

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