[Haskell] context rules for "default"

[Doug McIlroy]

What is the rationale for the requirement that, in order for
the ambiguous type of a numeric constant to be resolved by the
default declaration, all classes in the context must be in the
Standard Prelude or Standard Library (Revised Report 4.3.4)?
This makes it hard to introduce new polymorphic functions
whose domain includes the integers.

Doug McIlroy