On 06/04/2009, at 4:33 PM, Erick Tryzelaar wrote:
>>
>> The question is what 'x' means given
>>
>> var x = 1;
>
>
> To play the devils advocate, do we even need lvalues? I can live
> without pre and post incrementing.
What about assignment? If you can't get the address of a variable
you cannot modify its value.. are you sure you want to move to a
100% purely functional language? If so why not use Haskell or Erlang?
>
> if it'd make our semantics clearer. It'd also make sense if we ever
> actually made functions are purely functional, rather than just
> assumed they were.
Functions (funs) are required to be functional now, but they CAN depend
on variables so we do not have referential transparency ;(
In fact been thinking of
var x = 1;
pfun f() => x; // ERROR
> I think it makes sense to support mutation, but I
> don't think it needs to be transparently supported.
Probably the opposite, be nice to *see* where mutations are
done and require that, but even Haskell can't enforce that
(State monad effectively hides mutations by making them
dependent on type instead of syntax).
It's hard to see how to distinguish say functions and generators,
we'd have to have say
val x = f( @rand())
where the @ was mandatory (i.e. make all generators start with @ so you
can see them).
It all gets complex: there is more than one kind of generator, and
indeed kinds
of functions. For example you could be made to write
var x = 1;
fun f<x>()=>x;
to say f is pure *except* it refers to variable x, then
fun f<>()=>1;
is clearly marked pure and
fun f()=>x;
would be an error because pure is the default (missing <> defaults).
At least two kinds of generators too: ones that depend on external
state like system time, rand, etc, and ones only using internal
state -- the latter are predictable, and can be restarted by making
a new closure (typical example: iterators).
Which annotations to chose? Some mix of those giving visual strength
to the language reader, and those allowing better optimsations.
"purity" doesn't help with optimisations in Felix because Felix can
calculate if a function is pure or not anyhow (and does).
--
john skaller
skal...@users.sourceforge.net
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