On Mon, 2007-09-10 at 15:27 -0700, Erick Tryzelaar wrote:
> Also, since do-done are already keywords, we could make them
> synonymous with braces in this situation, so that we could reduce the
> foreach to this, which is much easier to read:
>
> d.foreach do |d:string|
> println d;
> done;
I'm thinking to make begin/end keywords. Begin/end mark a block,
and are equivalent to { } sometimes, like Ocaml.
do/done marks a loop or control structure *without* a scope,
i.e. it's labels and gotos.
So vaguely:
whilst c begin sts end;
==> whilst c do { sts }; done;
> I'm just not sure how we handle errors, though.
What errors?
If you make a programming error, and Felix detects it,
Felix aborts. This is right IMHO. It's a bug. Fix it!
Felix has a Zero Tolerance policy for bugs.
So .. if you say 'open f' and f doesn't exist, Felix
aborts, as it should. Otherwise use
let h = try_open f in match h with
| Failed => ...
| Handle h => ..
endmatch
Felix does 'exceptions' with some messiness. In procedures,
use a non-local goto:
proc f() {
proc exc(){ goto err; }
println "Stuff";
g (the exc);
return;
err:>
println "Error";
}
proc g(exc:1->0) {
...
exc(); // throw exception
throw exc; // throw exception
val x = h exc 1;
}
fun h(exc:1->0) (x:int)= {
if x<0 do throw exc; done;
return x;
}
You have to 'throw' an exception out of a function.
Throw really does use a C++ throw. Probably should make
fun throw[t]: (1->0)->t = "(?1) (throw (con_t*)$1)";
The problem with 'throw' is that it doesn't unwind
procedure stacks properly: it leaves the _caller variable
set, which means if there is a pointer to a variable in
the call chain, the chain is reachable and won't be collected.
Really, we should have call data= _caller + display including
pointer to data object, so unwinding the call data is always
safe, even if there is a pointer to some variable in the
stack frame .. however this would require TWO allocations.
BTW: _throw is a builtin primitive .. :)
Note that EH will be easier to do if we can ensure all
functions throwing are converted to heaped procedures;
unfortunately it's hard to tell if a closure (func or
proc passed as a value) throws.. it would have to be
made part of the type.
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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