[erlang-questions] Extensions to comprehensions eeps

Richard A. O'Keefe <>
Fri Aug 1 02:09:42 CEST 2008


On 31 Jul 2008, at 9:47 pm, Anthony Shipman wrote:
> People claim that an advantage of dynamic languages is that you  
> don't have to
> put type annotations on variables.  The language operations are, as  
> far as
> possible, polymorphic at run time.

In a decent language, not "as far as POSSIBLE",
but "as far as USEFUL/REASONABLE".

> So you can change the type of a variable
> and not have to go through the source updating type declarations  
> etc. This is
> supposed to make for more rapid prototyping.
>
> But then you get into the details of Erlang and find that there are
> effectively type annotations all over the place  to help the  
> compiler. They
> don't appear as explicit type annotations, they sneak in in the  
> punctuation.
>
> The existing <- vs <= is just as much an error.

As noted in a recent posting of mine,
there is a fundamental semantic difference between <- and <= .
It doesn't even begin to make anything approaching the shadow
of sense to exchange one for another.

Basically, lists *HAVE* elements, and the pattern in a list
generation plays no part in determining what the elements are.
But binaries do *NOT* have elements.  The pattern in a binary
generation *must* be a binary pattern and it is the pattern
which determines how the binary is chopped up.  One and the same
binary might result in 20 iterations using one pattern or 50
using another.

I have used programming languages that tried to allow every combination
that could possibly be given some twisted sort of sense.  I even
designed my own once.  I learned the hard way that this is NOT a help
to the programmer.

The things you call "type annotations" and imagine that they are
"to help the compiler" are there to help *people*.

Do you think that having <integer> / <integer> do div (as in C and
Fortran) would be *good* for programmers?

> I would like further
> development in Erlang to fix these errors rather than add many more  
> funny
> symbols. Otherwise the language would end up looking like haskell.

Nobody is talking about "many more funny symbols".
In fact, the thing that seems to have got up the noses of a couple of
people appears to be the fact that I chose to use combinations of
existing symbols *instead* of inventing a new symbol.

Be specific about what are the "errors" you are complaining of.

I note that Sun recently donated a fancy machine to the Haskell
community because Haskell is particularly good at both concurrency
and parallelism these days, and Sun want that on _their_ multicore
hardware, thank you!

Oddly enough, Haskell is *better* at letting you associate many
meanings with the same symbol than Erlang is.




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