Re: [Haskell-beginners] Re: mayBe stuck

On Fri, Aug 06, 2010 at 09:06:24PM -0700, prad wrote:

On Fri, 6 Aug 2010 13:38:56 +0100 Brent Yorgey wrote:

...

you shift the burden of proving that it is safe from the compiler onto yourself ... Here are some off the top of my head, for beginners reading this who might not already know:

fromJust head tail init last (!!)

i'm trying to follow this conversation. the problem is that some of these functions don't behave nicely for some inputs right? like tail []

All of these functions are "partial", which means that they are undefined (crash with an error) for some inputs. If possible you should try to program only with "total" functions (functions which are defined for every input) since then you know your program will not crash.

also, is it better to use pattern matching (x:xs) than head and tail? could that be part of the point here too?

Yes, that's exactly right. -Brent