Re: PartialFunction and Function

[Matthew Willson]

but PartialFunction extends Function (seems wrong way round, at least

according to the mathematical definition of function and partial

function).

http://lampsvn.epfl.ch/trac/scala/ticket/85

"equate PartialFunction with Function ?"

After lengthy discussion, this ticket is suddenly closed as invalid with

the transparency classic "After lots of discussion at EPFL, the group

has decided to keep things how they are." It comes up a lot.  Partials

are unnecessarily clumsy to use, and it's a bummer because they're so

freaking useful.

My thoughts on this:

The issue seems to be that really:

Function = "Partial function with no explicit information about which values it will terminate on"
PartialFunction = "Partial function with explicit information about which values it will terminate on"

So collapsing the two (PartialFunction and Function) into one class does make a lot of sense to me.

But perhaps the reason this wasn't done before is that this solution would leave you unable to distinguish between, eg:

* isDefinedAt  defined true everywhere as a kind of default fallback when no information was explicitly given about where the function terminates
* isDefinedAt intentionally defined true everywhere to communicate that the function was defined to terminate everywhere

So, my suggestion is to have an interface on Function which allows you to determine 2 things:
* Is explicit information available on whether the function terminates?
* If so, what is that information?

That interface could be like, eg:

def definedInformationAt(a : A) : Option[Boolean]

returning
Some(true) where the function is known/guaranteed to terminate on that value
Some(false) where the function is known/guaranteed not to terminate on that value
None where there's no explicit information about whether it terminates on that value.

Think that would help at all? worth suggesting on the ticket?

-Matt

[Matthew Willson-3]

but PartialFunction extends Function (seems wrong way round, at least

according to the mathematical definition of function and partial

function).

http://lampsvn.epfl.ch/trac/scala/ticket/85

"equate PartialFunction with Function ?"

After lengthy discussion, this ticket is suddenly closed as invalid with

the transparency classic "After lots of discussion at EPFL, the group

has decided to keep things how they are." It comes up a lot.  Partials

are unnecessarily clumsy to use, and it's a bummer because they're so

freaking useful.

The issue seems to be that really:

Function = "Partial function with no explicit information about which values it will terminate on"
PartialFunction = "Partial function with explicit information about which values it will terminate on"

So collapsing the two (PartialFunction and Function) into one class does make a lot of sense to me.

But perhaps the reason this wasn't done before is that this solution would leave you unable to distinguish between, eg:

* isDefinedAt  defined true everywhere as a kind of default fallback when no information was explicitly given about where the function terminates
* isDefinedAt intentionally defined true everywhere to communicate that the function was defined to terminate everywhere

So, my suggestion is to have an interface on Function which allows you to determine 2 things:
* Is explicit information available on where the function was defined to terminate?
* If so, what is that information?

That interface could be like, eg:

def definedInformationAt(a : A) : Option[Boolean]

returning
Some(true) where the function is known/guaranteed to terminate on that value
Some(false) where the function is known/guaranteed not to terminate on that value
None where there's no explicit information about whether it terminates on that value.

Think that would help at all? worth suggesting on the ticket?

-Matt