Proposal: Partial Type Signatures

[Thomas Winant]

On 13-03-14 10:46, Simon Peyton Jones wrote:
> | Together with Tom Schrijvers, Frank Piessens and Dominique Devriese, I
> | have been working on a proposal for adding *Partial Type Signatures* to
> | GHC.
>
> I'm all for this.  Yes, if the design and implementation are solid, I'd be happy to add it to the main branch.
>
> Do focus on something with excellent power-to-weight ratio: that is, gives a lot of benefit for a small cost, rather than something that gives 10% more benefit for 200% more cost.
>
> I've annotated the wiki page with some "SLPJ" comments, which you may want to look at.
>
> I'd be happy to have a Skype conversation about the details in due course.

Excellent, I added responses ("thomasw") to your comments on the wiki
page.

Cheers,
Thomas


> | -----Original Message-----
> | From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Thomas
> | Winant
> | Sent: 12 March 2014 13:36
> | To: ghc-devs at haskell.org
> | Cc: Tom Schrijvers; Frank Piessens
> | Subject: Proposal: Partial Type Signatures
> |
> | Dear GHC developers,
> |
> | Together with Tom Schrijvers, Frank Piessens and Dominique Devriese, I
> | have been working on a proposal for adding *Partial Type Signatures* to
> | GHC. In a partial type signature, annotated types can be mixed with
> | inferred types. A type signature is written like before, but can now
> | contain wildcards, written as underscores. The types of these wildcards
> | or unknown types will be inferred by the type checker, e.g.
> |
> |      foo :: _ -> Bool
> |      foo x = not x
> |      -- Inferred: Bool -> Boo
> |
> | The proposal also includes a form of generalisation which aligns with
> | the existing generalisation that GHC does. We have written down a
> | motivation (when and how might you use this) and details about the
> | design and implementation on the following wiki page:
> |
> | https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures
> |
> | We have a (work in progress) implementation [1] of the feature based on
> | GHC. It currently implements most of what we propose, but there are some
> | remaining important bugs mostly concerning the generalisation. We also
> | described our design and presented a formalisation based on the
> | OutsideIn(X) formalism in a paper [2] presented at PADL'14.
> |
> | What we are hoping to get from the people on this list is any of the
> | below:
> | * Read the design, play with the implementation and tell us any comments
> |    you may have about the feature, its design and implementation.
> | * Opinions on whether this feature might be acceptable in GHC upstream
> |    at some point (if not, we do not think it's worth developing the
> |    implementation much further).
> | * Perhaps a code review or a discussion with someone more knowledgeable
> |    about the internals of GHC's type checker about how we might fix the
> |    remaining problems in our implementation (specifically, we could use
> |    some help with implementing the generalisation of partial type
> |    signatures).
> | * Feedback on the `Questions and issues' section on the wiki page.
> |
> |
> | Kind regards,
> | Thomas Winant
> |
> | [1]: https://github.com/mrBliss/ghc-head/
> | [2]: https://lirias.kuleuven.be/bitstream/123456789/423475/3/paper.pdf
> |
> |
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