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Simon Peyton Jones authored
This patch finally adds 'left' and 'right' coercions back into GHC. Trac #7205 gives the details. The main change is to add a new constructor to Coercion: data Coercion = ... | NthCo Int Coercion -- OLD, still there | LRCo LeftOrRight Coercion -- NEW data LeftOrRight = CLeft | CRight Plus: * Similar change to TcCoercion * Use LRCo when decomposing AppTys * Coercion optimisation needs to handle left/right The rest is just knock-on effects.
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