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SUMMARY:Reasoning about GADT Pattern Matching in Haskell  - George Karacha
 lias\, Ghent University
DTSTART:20141022T130000Z
DTEND:20141022T140000Z
UID:TALK55356@talks.cam.ac.uk
CONTACT:Microsoft Research Cambridge Talks Admins
DESCRIPTION:Generalized Algebraic Data Types (GADTs) are a simple but powe
 rful generalization of Algebraic Data Types (ADTs) in Haskell and the ML f
 amily.\n\nReasoning about the accessibility of case branches and the exhau
 stiveness of pattern matching is a well studied and efficiently solved pro
 blem for ADTs. However\, classic algorithms fall short in the presence of 
 GADTs\, issuing false warnings: Since GADT constructors introduce local co
 nstraints\, we must allow for the fact that particular combinations of pat
 terns and/or values cannot actually occur. \n\nWe present a novel algorith
 m for checking pattern matching that accounts for Haskell's laziness and r
 elies on implication constraints generated and solved by the OutsideIn(X) 
 type inference engine. Since we rely on the existing type inference engine
 \, our approach is efficient and robust to future extensions of the type s
 ystem. We also report on a proof-of-concept implementation of our algorith
 m in GHC. \n
LOCATION:Auditorium\, Microsoft Research Ltd\, 21 Station Road\, Cambridge
 \, CB1 2FB
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