On Sun, Feb 1, 2015 at 2:27 PM, Paul Rubin <no.email@nospam.invalid> wrote: > Devin Jeanpierre <jeanpierr...@gmail.com> writes: >> That said, Haskell (and the rest) do have a sort of type coercion, of >> literals at compile time (e.g. 3 can be an Integer or a Double >> depending on how you use it.) > > That's polymorphism, not coercion.
OK, yes, that fits better into how Haskell works. After all, that's how "Nothing" works. If 3 is just a (magic) constructor, then it's no different. > The compiler figures out at compile > time what type of 3 you actually mean: there is never an automatic > runtime conversion. sqrt(3) works because sqrt expects a floating > argument so the compiler deduces that the 3 that you wrote denotes a > float. sqrt(3+length(xs)) has to fail because length returns an int, so > 3+length(xs) is an int, and you can't pass an int to sqrt. > >> BTW it's weird that in this thread, and in the programmer community at >> large, int->string is considered worse than int->float > > Hehe, though int->string leads to plenty of weird bugs. > >>> Haskell's idiomatic substitute for a null pointer is a Nothing value >> For that matter, how is this (first part) different from, say, Java? > > In Java, functions expecting to receve sensible values can get null by > surprise. In Haskell, if a term can have a Nothing value, that has to > be reflected in its type. Haskell's bug-magnet counterpart to Java's > null values is Bottom, an artifact of lazy evaluation. E.g. you can > write > x = 3 / 0 > someplace in your program, and the program will accept this and run > merrily until you try to actually print something that depends on x, > at which point it crashes. This isn't a difference in whether there are multiple nulls, though. I answered my own question later, by accident: Java nulls are castable to each other if you do it explicitly (routing through Object -- e.g. (Something)((Object) ((SomeOtherThing) null)))). So in that sense, there is only one null, just with some arbitrary compiler distinctions you can break through if you try hard enough. -- Devin -- https://mail.python.org/mailman/listinfo/python-list
