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Postings from August 2012
On Fri, Aug 24, 2012 at 10:30:49AM +1000, Damian Conway wrote: > But what about: > > is_prime( all(2,3) ) > > If the junction is passed in, is_prime() returns: > > all() # i.e. false > > which is wrong...whereas the "proper" semantics of: > > all( is_prime(2), is_prime(3)) > > produces: > > all(1,1) # i.e. true. > > So it's perfectly possible to have a sane and reasonable semantics for > junctions and a sane and reasonable semantics for is_prime(), that are > not sane and reasonable when used together. > > In fact, that's why junctive arguments are supposed to distribute across > subroutine calls, rather than be passed into them: because subroutines > that are not specifically designed for junctive arguments generally > break when passed junctive arguments (especially conjunctive arguments). > In exactly the same way that subroutines not designed for complex > numbers or surreal numbers, or matrices, or quaternions, generally don't > work correctly when passed those kinds of values. Subroutines are coded > assuming a particular arithmetic model, and data that doesn't follow > those particular rules just won't work right. Does that mean that we *ought* to be changing the calling conventions to spot junctions on the way in and multiplex a single call into multiple calls? This is how Perl 6 does it? What happens if we don't change that? ie that junctions are in @_, and a non-junction aware function is called? In what circumstances do things go wrong? Nicholas ClarkThread Previous | Thread Next