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When generating dictionary let binds in dsTcEvBinds we may end up generating them in arbitrary order according to Unique order. Consider: ``` let $dEq = GHC.Classes.$fEqInt in let $$dNum = GHC.Num.$fNumInt in ... ``` vs ``` let $dNum = GHC.Num.$fNumInt in let $dEq = GHC.Classes.$fEqInt in ... ``` The way this change fixes it is by using `UniqDFM` - a type of deterministic finite maps of things keyed on `Unique`s. This way when you pull out evidence variables corresponding to type-class dictionaries they are in deterministic order. Currently it's the order of insertion and the way it's implemented is by tagging the values with the time of insertion. Test Plan: I've added a new test case to reproduce the issue. ./validate Reviewers: ezyang, simonmar, austin, simonpj, bgamari Reviewed By: simonmar, simonpj, bgamari Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D1396 GHC Trac Issues: #4012
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