[<<][compsci][>>][..]Fri Oct 28 13:47:56 EDT 2011
Main idea is that multi-param type classes are relations = sets of
tuples, and can be seen as relational databases.
The basic problem with multi-param type classes is ambiguity. When
composing operations, it might be that some type parameters that are
in the constraints no longer appear in the right hand side. I.e.
TypeRel a b c => a -> b
Here 'c' is ambiguous. See [1] section 2.4 for examples.
[1] http://www.reddit.com/r/haskell/comments/7oyg5/ask_haskellreddit_can_someone_explain_the_use_of/
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