Currently, the .global directive for pir is unimplemented. Other than
being in the source code for the imcc compiler, it's absent. Is
.global intended to truely store to global, or be more like a mutable
constant, applicable to only that file(and then perhaps any that
.include it). If it's intended to be more like a macro, "global"
statics already have a a method to access them. For localized statics,
i.e. [3], I like the .static int var = 123 most for familiarity. As
for values, I'd say strings, floats, and ints can have a default value
writing in plain sight for them, but for pmcs they would need to be
initialized in an :immediate sub. E.g.
.global int foo = 42
.global pmc bar
.sub init :immediate
bar = new .FixedIntegerArray
bar = 4
.end
On Jan 30, 2006, at 8:54 AM, Leopold Toetsch wrote:
Below are some thoughts WRT C static vars and Perl6 INIT blocks.
Comments welcome,
leo
Supporting C static storage
There are some related Perl6 features, namely INIT and FIRST closure
traits [1], which aren't really covered by Parrot yet.
Parrot supports INIT blocks via :immediate, which allows e.g.
translation of:
constant Num pi = { atan(1,1)*4 }; # [2]
But C statics can of course change. The problems is, where to
store the static variable, especially native integers.
double gen_random(double max) { # [3]
static long last = 42;
...
}
We could use closures, coroutines [4], or globals. The former provide
a persistent register frame, where the static can be kept. Translating
a sub with a C static to a coroutine seems to be a bit unnatural
though. And all these solutions are a bit slow and lexicals/globals
are only providing PMC support.
I think, we should use the constant table and allow storing into
the constant table.
E.g.
.static int last = 42 # ldc_i_ic
(We can't use the C<set_i_ic> opcode, as this is loading constants
from the bytecode, which, when mmaped, is readonly and doesn't allow
storing)
last += 10 # add_i_ic / set_ic_i
.static float f = 3.14 # set_n_nc
f += 2.0 # add_n_nc / set_nc_n
f = 5.0 # set_n_nc / set_nc_n
.static .Integer i = "42" # set_p_pc
The 'static' variables are therefore working mostly like constants,
except that they are modifyable. One difference is of course, that
there would be no constant folding, each .static needs a distinct
storage in the constant table.
We'd need a few new opcodes:
ldc_i_ic # load int constant from constant table
set_ic_i # store int into constant table
set_nc_n # store num
assign_pc_p # assign to PMC static value
And maybe some permutations like set_pc_i.
What do you think?
leo
[1] S04 / Closure traits
[2] # t/pmc/sub_38.pir
.sub make_pi :immediate, :anon
$N0 = atan 1.0, 1.0
$N0 *= 4
$P0 = new .Float
$P0 = $N0
.return ($P0)
.end
.sub main :main
.const .Sub pi = "make_pi"
print pi
print "\n"
.end
[3]
http://shootout.alioth.debian.org/sandbox/benchmark.php?
test=random&lang=icc&id=0
[4] examples/shootout/random.pir
