i guess there's really two implicit arguments - the value's type, `a` (quantified via forall - the System F "Λ") and its vtable `Show a`... though i guess the v

i guess there's really two implicit arguments - the value's type, `a` (quantified via forall - the System F "Λ") and its vtable `Show a`... though i guess the vtable is uniquely determined by the type bc in Haskell instances are globally unique