[Haskell-cafe] Layout rules for if then else

[Alan & Kim Zimmerman]

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 at 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 at 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 at gmail.com>
>> wrote:
>>
>>> On Tue, Mar 10, 2015 at 12:01 PM, Alan & Kim Zimmerman <
>>> alan.zimm at 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 at gmail.com
>>> ballbery at sinenomine.net
>>> unix, openafs, kerberos, infrastructure, xmonad
>>> http://sinenomine.net
>>>
>>
>>
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>
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