Named instances for Core Solidity

[rodrigogribeiro]

This PR introduces named instances for Core Solidity, following the approach used by Idris.

[Y-Nak]

Proposal: Named instances for Core Solidity

[mbenke]

If an instance has the same name as a function, the compiler says the name is undefined, e.g.

// named instance/function name conflict

forall a.class a:C {}

instance [foo] word : C {}

function foo(x:word) { 7 }

contract Clash {
  function main() -> word {
    return foo(1);
  }
}

Module validation failed for /home/ben/work/review/tmp/named4.solc:
Undefined name: foo
 - in:return foo(1) ;
 - in:function main () -> word {
   return foo(1) ;
}

[mbenke]

Nicely done. I do not want to appear nitpicky but there still are some problems with case sensitivity:

forall a . class a : Eq {
  function upperScore(x : a) -> word;
}

forall a . class a : eq {
  function lowerScore(x : a) -> word;
}

forall a . a : Eq, a : eq => function useBoth(x : a) -> word {
  return Eq.upperScore(x);
}

instance [upperEq] word : Eq {
  function upperScore(x : word) -> word {
    return 1;
  }
}

instance [lowerEq] word : eq {
  function lowerScore(x : word) -> word {
    return 2;
  }
}

contract NamedInstSlotOrderSensitivity {
  function main() -> word {
    return useBoth@{eq = lowerEq, Eq = upperEq}(1);
  }
}

yields

test/examples/cases/named-inst-slot-order-sensitivity.solc
Constraint slot eq matches multiple wanted constraints for useBoth
Use a class name with exact capitalisation to disambiguate.

Of course it is not a good idea to have class names differing only in capitalisation, but I can imagine this happening with imports.

[Y-Nak]

@mbenke Thank you for the review; it's helpful.
I fixed the issue that you found. Would you review it again?