HIE Files

[Zubin Duggal]

>
> And that in turn raises the questions of WHAT syntax tree.  HsSyn?
> Template Haskell?  Haskell-src-exts?  Or something new?   Shayan and Alan
> are busy parameterising HsSyn to make it non-GHC-specific, and directly
> usable for this kind of endeavour ("Trees that grow").  It'd be great to
> build on their work.


Mainly, we need information on every Token that appears in the original
source. My plan is to further group Tokens into a simple rose-tree based on
how they occur in HsSyn. We intentionally want to avoid capturing too much
information so the format doesn't change much with changes to the GHC AST.

I've made a file describing roughly what the data structures involved
should look like

https://gist.github.com/wz1000/edf14747bd890b08c01c226d5bc6a1d6

The plan is to group the Tokens together in a tree in way similar to what
structured-haskell-mode does. (The gifs in the following link might provide
some idea)

https://github.com/chrisdone/structured-haskell-mode/

For example, here is what structured-haskell-mode outputs for a small
snippet of code:
https://gist.github.com/wz1000/db42d4f533ba7d2345934906b312f743

We want something similar for the HIE AST, but grouped into a tree, where
each node(roughly corresponding to HsSyn constructors) points to all the
subnodes and tokens it spans over.

That's great.  But would it not be good to offer a library, with a
> well-defined API, that allows a client (including Haddock) to parse those
> .hie files into syntax trees or whatever?  You'll need to do that to allow
> the haddock thing you describe -- and it'd be much better to make the
> parser (and doubtless lots of utility function like finding things in the
> tree) available to any client not just haddock.
>

Yes, a library to consume these files is definitely something we need, and
I believe it will grow out naturally as we work out the integration with
haddock and haskell-ide-engine.

On 15 May 2018 at 14:12, Simon Peyton Jones <simonpj at microsoft.com> wrote:

> |  > Why not put the .hie-file info into the .hi file?  (Optionally, of
> |  > course.)
> |  >
> |
> |  Simon, I'm curious what benefits you think we might get from this?
> |  (I'm one of the mentors on this GSoC project btw).
>
> Well, I've always thought that we should really put the .hi file into the
> .o file!  Having two files risks getting things out of sync, and three
> makes that worse.  The file is just a place to keep a blob of info.  What's
> the motivation for having two .hie as well as .hi?
>
> |
> |  > What tools/libraries do you plan to produce to allow clients to read
> |  a .hie file and make send of the contents?
> |
> |  For GSoC as a proof of concept the idea is to teach haddock's
> |  hyperlinked-source backend to use this information to add type-
> |  annotation-on-hover to the colorized, hyperlinked, html source.
>
> That's great.  But would it not be good to offer a library, with a
> well-defined API, that allows a client (including Haddock) to parse those
> .hie files into syntax trees or whatever?  You'll need to do that to allow
> the haddock thing you describe -- and it'd be much better to make the
> parser (and doubtless lots of utility function like finding things in the
> tree) available to any client not just haddock.
>
> And that in turn raises the questions of WHAT syntax tree.  HsSyn?
> Template Haskell?  Haskell-src-exts?  Or something new?   Shayan and Alan
> are busy parameterising HsSyn to make it non-GHC-specific, and directly
> usable for this kind of endeavour ("Trees that grow").  It'd be great to
> build on their work.
>
> |  with the GHC API. (This by the way is one of the key benefits of
> |  keeping the file separate from standard hi files -- it should be
> |  parseable and consumable without needing to link in GHC).
>
> Yes, not linking in GHC is a reasonable goal; but having two files and
> file formats is not a necessary consequence of that goal.  Nothing stops us
> making a library to parse .hi files -- indeed the entire iface/ directory
> in GHC is quite well separated for that precise purpose.
>
> None of this is to criticise the plan.  I think it's a great idea to make
> more info more readily available to more tools.   I'm just poking at it a
> bit 😊.
>
> Simon
>
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