Question

Can somebody please explain (with example) the difference between context-independent and context-dependent overloading?

Answer 1

I have never heard about those. And there’s only about five hits on Google, one of which is this very question, which seems to suggest to me that these are made-up terms. And as with any made-up term, if you want to know what it means, you have to ask the person who made it up.

From what little I could gather, it seems to be related to return-type based overloading.

Basically, if you have four overloaded functions like these:

foo :: string → int
foo :: string → string
foo :: string → ()
foo :: int → int

And you call them like this:

1 + foo 1
1 + foo "one"
foo "one"

Then, with context-dependent overloading (i.e. overloading based on the return type as well as the parameter types), the following implementations will be selected:

1 + foo 1     # foo :: int → int
1 + foo "one" # foo :: string → int (because `+` takes an `int`)
foo "one"     # foo :: string → ()  (because there is no return value)

Whereas with context-independent overloading (i.e. ignoring the return type), the following implementations will be selected:

1 + foo 1     # foo :: int → int
1 + foo "one" # ERROR
foo "one"     # ERROR

In both the ERROR cases, there is an ambiguity between foo :: string → int, foo :: string → string and foo :: string → (), since they only differ in their return type but have the same paremeter type.