Fix ambiguity error in command
function
#48
Merged
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Running the following command in GHCi gives an interesting error message
GHC complains about some
c0
type variable that doesn't appear anywhere else. Interestingly, this only appears for certain types. If we replaceMember
withInt
then it typechecks.After some digging, the culprit seems to be
Aha! We've introduced a new type variable
c
that's unrelated to the one mentioned in the type signature ofcommand
, leading to the ambiguity error.ParameterParser
in turn requiresParameterParser
in certain instances. Namely, the instances for types that cause the expression to not typecheck (such asMember
).The fix is simple, add
c
to the typeclass parameters ofParameterInfoForParsers
to ensure it's the samec
.