"Strong typing vs. strong testing"

Pascal Costanza pc at p-cos.net
Tue Oct 5 11:13:20 CEST 2010


On 05/10/2010 05:36, salil wrote:
> On Sep 30, 1:38 pm, Lie Ryan<lie.1... at gmail.com>  wrote:
>> The /most/ correct version of maximum() function is probably one written
>> in Haskell as:
>>
>> maximum :: Integer ->  Integer ->  Integer
>> maximum a b = if a>  b then a else b
>>
>> Integer in Haskell has infinite precision (like python's int, only
>> bounded by memory), but Haskell also have static type checking, so you
>> can't pass just any arbitrary objects.
>>
>> But even then, it's still not 100% correct. If you pass a really large
>> values that exhaust the memory, the maximum() could still produce
>> unwanted result.
>>
>> Second problem is that Haskell has Int, the bounded integer, and if you
>> have a calculation in Int that overflowed in some previous calculation,
>> then you can still get an incorrect result. In practice, the
>> type-agnostic language with *mandatory* infinite precision arithmetic
>> wins in terms of correctness. Any language which only has optional
>> infinite precision arithmetic can always produce erroneous result.
>
>
> I have not programmed in Haskell that much, but I think Haskell
> inferences type "Integer" (the infinite precision) by default and not
> "Int" (finite precision) type for the integers. So, the programmer who
> specifically mentions "Int" in the signature of the function, is
> basically overriding this default behavior for specific reasons
> relevant to the application, for example, for performance. I think
> Haskell's way is the right. It is providing "safe behavior"  as
> default and at the same time treating programmer as adults, at least
> in this case.
>
> I think dynamic languages are attractive because they make programs
> less verbose. But, statically typed languages with type inference
> (Haskell, OCaML, Scala, F#) is a very good compromise because they
> offer both type safety and succinctness. And when we need algorithms
> that should work the same independent of types, Haskell has
> typeclasses which are pretty intuitive, unlike the horrible C++
> templates.

Static typing still doesn't mesh well with certain kinds of reflection.


Pascal

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