[Haskell-cafe] Equality constraints and RankNTypes - how do I assist type inference

[Brandon S Allbery KF8NH]

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On 8/20/10 16:08 , DavidA wrote:
> type Tensor u v =
>     (u ~ Vect k a, v ~ Vect k b) => Vect k (TensorBasis a b) -- **

IIRC this actually substitutes as

  (forall k a b. (u ~ Vect k a, v ~ Vect k b) => Vect k (TensorBasis a b))

and the implicit forall will generally mess things up because it won't be
floated out to the top level.  (Or in other words, constraints in type
declarations don't generally do what you intend.)

- -- 
brandon s. allbery     [linux,solaris,freebsd,perl]      allbery at kf8nh.com
system administrator  [openafs,heimdal,too many hats]  allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university      KF8NH
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