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Hi, On Nov 28, 2011, at 14:03 , Neil N. Carlson wrote: > > I'm not actually surprised that the argument expression > was fully evaluated; that would be required if > merge were a user-function. Do intrinsic functions > have special rules in this regard? No. > > That got me to wondering why this bit of code doesn't > cause any problems with the other compilers we use, > which do trap on fp exceptions by default. Poking > around with the nag compiler, I've found that it > compiles the merge to a loop that only evaluates those > elements of the array expression that are used, and > so never tries to do a 1.0/0.0. I'd guess that the > other compilers are doing the same thing. Yes. > > I actually prefer this behavior (in this case at least), > but I'm suspicious that this may not be strictly kosher. It isn't. This has been discussed at length in J3/WG5 meetings. The difficulty is that expression evaluation goes to the heart of a compiler's optimizations. Thus, changes to the standard in this area must be made carefully. There was a proposal for f08 to add a "chooser" feature, which would satisfy the don't-evaluate-this-yet desire. But no one design emerged as clearly best, and there was a lack of time and people to fully explore things. IIRC, the two designs were a pseudo-function and a pseudo-operator. Neither could be seen as clearly better than the other. -- Cheers! Dan Nagle