On Tue, 2006-09-05 at 11:07 -0400, Peter Tanski wrote:
> On Sep 4, 2006, at 6:50 AM, skaller wrote:
> > BTW: also note this won't work in Felix at present,
> > because flxPty tried to start work before tanski woke up :)
>
> I had to read this several times and force myself to believe you are
> serious.
Executable code is executed in order of writing.
Variable declarations:
var x = 1;
are also executable. This is not a 'definition' of a synonym
for '1', it is an assignment:
var x: int;
x = 1; // assignment
> This isn't remotely functional-program behavior.
Felix is a procedural/imperative language with
a functional subsystem.
Note that 'val' is different:
val x = 1;
is more 'functional'. however at present, vals are
NOT reordered based on dependencies, instead they're
reordered based on what the optimiser thinks will
improve performance without breaking the sequential
semantics.
> > Generally, expressions are eagerly evaluated, statements
> > are executed in order of writing, and finally variant
> > constructors always make a heap copy of their argument:
> > so you'd be copying an uninitialised variable.
>
> This is not in the documentation
I know. Felix actually has 'indeterminate' evaluation order.
Sometimes it is eager and sometimes lazy. It depends on the
construct. At least this is the present scenario; in some
cases it isn't clearly defined. When you write a var:
var x = ...
it is sure to be assigned the RHS eagerly. If you write
val x = ...
it is up to the compiler to choose when to evaluate the RHS.
If you want lazy, you can now write:
fun x = ...
and the RHS is guaranteed to be lazily evaluated (it is
implemented with a closure which is invoked on each use).
And you can have another form:
ref x = ...
which is semi-lazy: a ref is a pointer which is dereferenced
on each use (so the value of x can change if the referent
is mutable and is modified).
> and the declaration of Felix as a
> "functional" language puts a programmer off guard to expect such
> behavior.
Who said it was functional? My claim is that it is a traditional
but advanced procedural language, with a functional
subsystem.
If you want 'functional' in the ML sense you can write:
var k =
let ?x =
let ?a = 1 in
let ?b = a + 1 in
a +b
;
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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