Just a waring about type constraints: they don't propagate.
I tried this in the library:
typedef i_schannel[t] = typesetof(ischannel[t], schannel[t]);
proc _read[t,CHAN:i_schannel[t]](chan:schannel[t],loc:&gcptr[t]) {
svc$ svc_sread$ cast[_schannel] chan, reinterpret[&gcaddress] loc;
}
proc read[t,CHAN:i_schannel[t]](v:&t,chan:CHAN) {
var x: gcptr[t];
_read(chan,&x);
*v = *x;
}
and it failed. I looked for a bug in the compiler, but there isn't
one: the bug is in the code.
The term:
CHAN:i_schannel[t]]
in the type variables list for 'read', says that CHAN is a type
variable, and there is a constraint
CHAN in typesetof(ischannel[t], schannel[t])
When a call is written, eg:
read (&x,ch)
the types t and CHAN are deduced from the arguments. Then,
the constraint is checked.
Now when the inner call in read is made to _read,
the call:
_read(chan,&x)
has signature
_read: CHAN * &t
This does matches _read, but the constraint of _read is NOT
satisfied because CHAN is a type variable. The binding
*inside* the read routine is fully polymorphic: it is bound
independently of any calls.
Even if you wrote:
_read[t,CHAN]
is wouldn't help: the constraint on CHAN in the parameter
list is NOT passed on to _read: it's a constraint on
the type variable, but it isn't part of the type.
It is very important to note this because this:
proc read[t,CHAN:i_schannel[t]](v:&t,chan:CHAN) {...
can actually be rewritten in sweeter form:
proc read[t](v:&t,chan:!i_channel[t]) {...
so it looks like i_channel[t] is a type .. the '!' char
there shows it isn't, its a constraint on a generated
type variable: working example:
fun f:!fast_ints * !fast_ints -> int = "int($1+$2)";
print$ f$ 1,2; endl;
--
John Skaller <skaller at users dot sf dot net>
Felix, successor to C++: http://felix.sf.net
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