There appears to be a bug in GCC (all versions up to and including
4.3.x) concerning exception handling on the Alpha.  This may be
related to

  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8966

Strictily speaking, the PPL uses exception handling, so if that does
not work on the Alpha, then the PPL does not work on the Alpha.  And
there is nothing to do but fix the GCC bug.

However, if that GCC bug really only affects exception handling and nothing
else, given that the PPL only uses exceptions for error reporting, we can
probably say that the PPL works on the Alpha *apart* from error reporting.
In other words, under this hypothesis (which we have no way to check),
users that are not interested in catching exceptions thrown by the PPL
(in response to invalid arguments, heap exhaustion, overflows, ...)
should probably not worry.  Your mileage may vary...