Friends
Many of you will know that I've been muttering about re-engineering GHC's type
inference engine for some time now. Dimitrios, Tom, Martin and I have just
completed an epic paper describing the Glorious New Framework that forms the
substance of the above mutterings:
http://haskell.org/haskellwiki/Simonpj/Talk:OutsideIn
We'd love comments and feedback. Dimitrios and I plan to roll up our sleeves
and implement it in June.
Simon
Modular type inference with local assumptions: OutsideIn(X)
Abstract. Advanced type system features, such as GADTs, type classes, and type
families have have proven to be invaluable language extensions for ensuring
data invariants and program correctness among others. Unfortunately, they pose
a tough problem for type inference, because they introduce local type
assumptions.
In this article we present a novel constraint-based type inference approach for
local type assumptions. Our system, called OutsideIn(X), is parameterised over
the particular underlying constraint domain X, in the same way as HM(X). This
stratification allows us to use a common metatheory and inference algorithm.
Going beyond the general framework, we also give a particular constraint solver
for X = type classes + GADTs + type families, a non-trivial challenge in its
own right.
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