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Simon Peyton Jones authored
The constraint (~) used to be (effectively): class a ~~ b => (a :: k) ~ (b :: k) but, with this patch, it is now defined uniformly with (~~) and Coercible like this: class a ~# b => (a :: k) ~ (b :: k) Result: * One less superclass selection when goinng from (~) to (~#) Better for compile time and better for debugging with -ddump-simpl * The code for (~), (~~), and Coercible looks uniform, and appears together, e.g. in TysWiredIn and ClsInst.matchGlobalInst. Previously the code for (~) was different, and unique. Not only is this simpler, but it also makes the compiler a bit faster; T12227: 9% less allocation T12545: 7% less allocation This patch fixes Trac #15421
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