[Haskell-beginners] Inferring functions from parameter types

[Russ Abbott]

Is there any theoretical reason why GHC (or Haskell) doesn't permit
functions to be inferred from their parameter types?

For example, if I write

null Data.Set.empty

I get a diagnostic saying


Ambiguous occurrence `null'
    It could refer to either `List.null', imported from Data.List at ...
                          or `Map.null', imported from Data.Map at ...
                          or `IntSet.null', imported from Data.IntSet at ...


Why doesn't GHC figure it out?

More generally it would be nice to be able to define:

f :: Type1 -> ResultType1
f :: Type2 -> ResultType2


and expect GHC to select the appropriate f based on the argument and implied
result types. Even if the type can't always be determined, why not do it
when possible and issue a complaint when it can't?

*
-- Russ *
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