On Fri, 30 May 2008 17:19:54 -0700, "Philip Weaver"
Dear Philip, could you point your virtual finger towards a reference/paper/book/any-bleeping-thing that would help this simple beginner understand why it doesn't work in this case? I'm trying to picture why a "read" function that terminates the program would be useful anywhere. In fact, any library function other than something like UNIX's "exit" or "kill" which terminates my program is not really welcome in any of my computer programs, but then again, I haven't yet been illuminated by the genie of pure functional languages. A reference would be awesome.
Sorry, I wouldn't know where to point you, other than stating the simple rule that you can't catch exceptions in pure code. Others may be able to enlighten you better.
By the way, the example that Dons gave may look more verbose, but (when possible) it's a probably a better idea to capture failure in a Maybe than in IO. I gave you "readIO" because it fit in to the exception handling that you were trying to do, and because you said you didn't want anyone to tell you you were doing things wrong :).
Here is a private reply from another user, which is more explanatory, the problem was that the read function wasn't getting called at a point where it could have been caught (I'll have to look into that into more detail): All you need is a little strictness, x <- (C.catch (return $! read line :: Int) (\e -> getNum)) works. Another option is using evaluate instead of return. The problem is that (read line :: Int) is not evaluated until it is needed, that is when it's going to be printed, but then it's too late to catch the exception. Some general remarks: hGetLine stdin === getLine do x <- action return x is the same as action