Re: GHC allow-overlapping-instances (PART II)

Am Freitag, 3. Oktober 2003, 10:22 schrieb Kenny:

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But how about instance C (AND (OR r1 r2) (OR r1 r2)) (OR r1 r2) --[1]

instance ( C (AND r1 r3) r5 , C (AND r2 r4) r6 ) => C (AND (OR r1 r2) (OR r3 r4)) (OR r5 r6) --[2]

GHC allows this with -fallow-overlapping-instances flag on, but why? Is [1] more specific than [2] or the other way round?

RTFM, i.e., the GHC User's Guide. Which instance is considered more special depends only on what comes after the class identifier, i.e., it does not depend on the context. So [1] is more special.

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Wolfgang