On 03/08/2014, at 4:16 PM, Jeffrey Beu wrote:
> Having a look a Felix I came away really impressed. Love the array type
> signature/definition/constructor.. whatever it is called. It seems a really
> thought out language - not sure about the generator business - that
> integrates with C/C++, seems almost perfect.
It was designed to leverage C/C++ libraries (although support for OO is weak).
in Felix functions are not allowed to have side effects.
For example:
var y = 1;
fun f(x:int) : int =
{
++y;
return y + x;
}
This is not allowed. You are supposed to use a procedure instead:
proc g (x:int, result: &int)
{
++y;
result <- y + x;
}
However this is so clumsy to use:
var result: int;
g (1);
// now we can use result in an expression
and it make binding C functions that DO have side effects quite hard.
For example .. ALL of Posix. So I decided to allow a special kind of
function with side effects, called a generator:
gen f(x:int) : int =
{
++y;
return y + x;
}
Generators can be used in an expression. When used directly:
var something = 1 + f (42) * 6;
Felix promised to lift the generator out like this:
var tmp = f (42);
var something = 1 + tmp * 6;
so it cannot be evaluated more than once. Generator expressions are
"unravelled" into
assignments to temporaries in a fixed order (namely, by recursive descent
analysis of
the expression) so any interaction between the side effects is deterministic.
The exemplar generator is rand(). But here's another one:
var init = 0;
gen fresh() = { var tmp = init; ++init; return tmp; }
which generates a sequence of integers, i.e. a fresh integer
on each call.
> My questions are does it work
It works .. modulo the usual bugs any system has.
> and will I have problems with the runtime on these mobile platforms
I have a friend that got Felix to build for various variants of iPhone
platforms.
Now, recently, the run time driver code was changed as follows:
previously, Felix ran its own driver loop. This would schedule
the fibres. It also interfaced to the async I/O system.
however many platforms, for example many GUI systems,
and many cases where you're running an event loop for
some reason and want to add Felix into the system, demand
THEY are the master. There's no point running a master Felix
loop inside a callback of an external event loop and losing all
the state at the end of the function.
So the driver was rewritten to use callbacks and a state object,
so you can now embed Felix inside a foreign event loop,
in the IDLE-TASKS callback or some other place you want.
Of course this is a C/C++ coding job you have to do to get
it embedded.
Now as to Android I don't know BUT, Felix works with SDL,
and SDL has the initialisation code for Windows, Linux,
OSX, Android, and iOS. All the hell interfacing C code to
Java has been done in SDL. Of course Android isn't Java,
its Linux, so underneath its all C, curses on Google for using
a Java API but there you go :)
> - it is the threads/asnyc stuff that has me concerned.
You do not have to use the async stuff. It is optional.
There are actually two drivers:
flx_run
flx_arun
The flx_run driver does not do any async I/O.
The flx_arun driver loads the async I/O library on demand.
It does this because if you use this driver, but actually don't
do any async I/O, it saves the overhead of starting the
event polling thread.
On the other hand, threading at the moment is mandatory.
The GC has two variants: a non-thread safe one and a thread
safe wrapper. The drivers use the thread-safe wrapper. At present
there's no way to avoid it, although it should be easy to do.
Unfortunately there is coupling between threads and the GC,
so that the GC library has mutexes etc in it, even if you do not
use the thread safe collector, the code for both GC variants is
in the same library. Any help decoupling the code would be
great.
So the answer to the thread issue is that at the moment it cannot
be avoided even if you don't use any threads, but in principle
it shouldn't be hard to split up the code so a basic non-threading
Felix could be used.
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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