arbitrary rank polymorphism and ghc language pragmas
Hi All: I've been working through some details in these papers [1], [2] and noticed a language pragma configuration that I hope you can confirm. When using explicit foralls in a data constructor, it appears that GHC 7.4.2 requires Rank2Types in the Language pragma for what the papers consider rank 1 types. Here's an example: data T = TC (forall a b. a -> b -> a) Am I correct, or is there another extension? The ExplicitForAll does not appear to support rank 1 types in data constructors. 1. Practical Type Inference for Arbitrary-Rank Types. 2. A Direct Algorithm for Type Inference in the Rank 2 Fragment of the Second-Order Lambda Calculus. -- Rick
At Thu, 05 Jul 2012 11:18:00 -0400, rickmurphy wrote:
data T = TC (forall a b. a -> b -> a)
The type of `TC' will be `(forall a b. a -> b -> a) -> T', a Rank-2 type. -- Francesco * Often in error, never in doubt
Thanks Francesco. And I did verify that ExplicitForAll does in fact allow Rank 1 Types in functions like the following ... f :: (forall a. a -> a) -- Rick On Thu, 2012-07-05 at 16:28 +0100, Francesco Mazzoli wrote:
At Thu, 05 Jul 2012 11:18:00 -0400, rickmurphy wrote:
data T = TC (forall a b. a -> b -> a)
The type of `TC' will be `(forall a b. a -> b -> a) -> T', a Rank-2 type.
-- Francesco * Often in error, never in doubt
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On 05/07/12 17:18, rickmurphy wrote:
Hi All:
I've been working through some details in these papers [1], [2] and noticed a language pragma configuration that I hope you can confirm.
When using explicit foralls in a data constructor, it appears that GHC 7.4.2 requires Rank2Types in the Language pragma for what the papers consider rank 1 types.
Here's an example:
data T = TC (forall a b. a -> b -> a)
Am I correct, or is there another extension? The ExplicitForAll does not appear to support rank 1 types in data constructors.
There is the PolymorphicComponents extension precisely for this use case. Twan
participants (3)
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Francesco Mazzoli -
rickmurphy -
Twan van Laarhoven