Fix break rewrite rules #71
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Previously these were matching on (==), which was rewritten by the class op rule before the breakByte rule had an opportunity to fire (haskell#70). Unfortunately fixing this requires that we change the Eq instances provided by GHC. This has been done in GHC 8.0.1 (base-4.9.0).
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The rewrite rules of
Data.ByteString.breakare currently quite fragile (see GHC #11688 and #70) as they match on the(==)class method. Class methods call-sites at known types are subject to GHC-generated "Class Op" rewrite rules, which rewrite the call-site to a call directly to the appropriate instance's implementation. These rules fire rather early in simplification and therefore defeatbytestring'sbreakrule.The usual solution here is to give each particular instance's implementation of
(==)a name which can be specifically matched (e.g.Int's(==)is defined in terms ofGHC.Classes.eqInt). Unfortunately, such names were previously not available forWord8. This will be fixed in GHC 8.0 (as of D1980). This branch rewrites thebreakrules to match on these new functions, which should make them far more robust.The second patch is merely a whitespace cleanup.