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Changes between Version 19 and Version 20 of Proposals/transformers

v19	v20
106	106	This usually means that the instance you're defining is now defined in the {{{transformers}}} package. You may wish to check it's the same, so you can just delete it.
107	107
108		''Could not deduce (Functor m) from the context (Monad m)''
109		This will be in a situation where you're using a monad constructed with a transformer as a Functor. If this is triggered by a use of {{{fmap}}}, you can replace it with {{{liftM}}} and the code will build with old and new versions of mtl. Alternatively, you can replace the {{{Monad m}}} with {{{Functor m}}} to make it work with mtl-2, or add a {{{Functor m}}} constraint to make it work with old and new versions of mtl.
	108	''Could not deduce (Functor m) from the context (Monad m)[[BR]]arising from a use of fmap''
	109	This will be a situation where you're using a monad constructed with a transformer as a Functor. You can replace {{{fmap}}} with {{{liftM}}} and the code will build with old and new versions of mtl.
	110
	111	''Could not deduce (Functor m) from the context (Monad m)[[BR]]arising from the superclasses of an instance declaration''
	112	This will be another situation where you're using a monad constructed with a transformer as a Functor. You can replace the {{{Monad m}}} with {{{Functor m}}} to make it work with mtl-2, or add a {{{Functor m}}} constraint to make it work with old and new versions of mtl.
110	113
111	114	''Not in scope: data constructor State''