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From: Devin Jeanpierre <jeanpierreda@gmail.com>
Date: Sun, 1 Feb 2015 14:52:22 -0800
Subject: Re: Python is DOOMED! Again!
To: Paul Rubin <no.email@nospam.invalid>
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On Sun, Feb 1, 2015 at 2:27 PM, Paul Rubin <no.email@nospam.invalid> wrote:
> Devin Jeanpierre <jeanpierreda@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