Take care!
There is a bug in the compiler causing
test/regress/rt/generators-01.flx
to fail. When I looked at the test I saw the problem instantly.
Here's the code:
///////////////////////////////////////////////////////
//Check generators
var cheat : int = 0;
gen f():int = {
++cheat;
//print "Generator "; print cheat; endl;
return cheat;
}
print "F 1="; print$ f(); endl; // 1
body """
static int x = 0;
int g() { ++x; return x; }
""";
gen g : 1 -> int;
print "C 1="; print$ g(); endl; // 1
fun d(x:int) => x + x;
// all these should be even
print "F Even? "; print$ d(f()); endl; // 4
print "F Even? "; print$ d(f()); endl; // 6
print "C Even? "; print$ d(g()); endl; // 4
print "C Even? "; print$ d(g()); endl; // 6
print "F 4="; print$ f(); endl; // 4
print "C 4="; print$ g(); endl; // 4
/////////////////////////////////////////////////
and the output:
F 1=1
C 1=1
F Even? 4
F Even? 6
C Even? 5
C Even? 9
F 4=4
C 4=6
Obviously, C is wrong: 5 and 9 are not even! Should read 4 and 6!
The problem is simple: the primitive generator g() is wrapped in a
plain (non-generator) function. Since that function isn't marked as
a generator as it should be, the x+x is replaced by the wrapper
in both cases of x. Were the wrapper of g ALSO marked as a generator
it would be hauled out of the expression and assigned ONCE to a variable
which is then added to itself.
So the bug is simple: the wrapper of a primitive should inherit the
primitives generator attribute. Easy fix.
But this suggests I issue a warning! Generator have side effects
and they can NOT be nested in a function, only in a generator
or procedure (except in special circumstances where you can
prove it is harmless).
--
john skaller
[email protected]
http://felix-lang.org
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