1. 12 Jan, 2017 1 commit
  2. 12 May, 2015 1 commit
    • David Terei's avatar
      New handling of overlapping inst in Safe Haskell · 4fffbc34
      David Terei authored
      We do much better now due to the newish per-instance flags. Rather than
      mark any module that uses `-XOverlappingInstances`,
      `-XIncoherentInstances` or the new `OVERLAP*` pragmas as unsafe, we
      regard them all as safe and defer the check until an overlap occurs.
      
      An type-class method call that involves overlapping instances is
      considered _unsafe_ when:
      
      1) The most specific instance, Ix, is from a module marked `-XSafe`
      2) Ix is an orphan instance or a MPTC
      3) At least one instance that Ix overlaps, Iy, is:
         a) from a different module than Ix
         AND
         b) Iy is not marked `OVERLAPPABLE`
      
      This check is only enforced in modules compiled with `-XSafe` or
      `-XTrustworthy`.
      
      This fixes Safe Haskell to work with the latest overlapping instance
      pragmas, and also brings consistent behavior. Previously, Safe Inferred
      modules behaved differently than `-XSafe` modules.
      4fffbc34
  3. 31 Jul, 2014 1 commit
    • Simon Peyton Jones's avatar
      Complete work on new OVERLAPPABLE/OVERLAPPING pragmas (Trac #9242) · 1ae5fa45
      Simon Peyton Jones authored
      * Deprecate -XOverlappingInstances
      
      * Update test suite.  Several tests even had entirely unnecessary
        uses of -XOverlappingInstances
      
      * Update user manual with a careful description of the instance
        resolution story
      
      * Fix an outright bug in the handling of duplidate instances in GHCi,
        which are meant to silently overwrite the earlier duplicate. The
        logic was right for family instances but was both more complicated,
        and plain wrong, for class instances.  (If you are interested, the
        bug was that we were eliminating the duplicate from the InstEnv, but
        not from the [ClsInst] held in tcg_insts.)  Test is ghci044a.
      1ae5fa45
  4. 25 Oct, 2011 1 commit