Optional Static Typing - Haskell?

[Alex Martelli]

Neal D. Becker <ndbecker2 at verizon.net> wrote:

> I've just started learning about Haskell.  I suggest looking at this for an
> example.
> 
> A good intro: http://www.haskell.org/tutorial

Haskell's a great language, but beware: its static typing is NOT
optional -- it's rigorous.  It can INFER types for you (just like, say,
boo), that's a different issue.  It also allows bounded genericity at
compile time (like, say, C++'s templates without the hassles), and
that's yet another (typeclasses are a great mechanism, btw).

Languages with really optional static typing can be found; I think the
premier example is still Dylan -- a kind of commonlisp without infix
notation, unfortunately very out of fashion nowadays but still available
(some good books, too).

I love the explanations of Van Roy and Haridi, p. 104-106 of their book,
though I may or may not agree with their conclusions (which are
basically that the intrinsic difference is tiny -- they point to Oz and
Alice as interoperable languages without and with static typing,
respectively), all the points they make are good.  Most importantly, I
believe, the way dynamic typing allows real modularity (harder with
static typing, since type discipline must be enforced across module
boundaries), and "exploratory computing in a computation model that
integrates several programming paradigms".

"Dynamic typing is recommended", they conclude, "when programs must be
as flexible as possible".  I recommend reading the Agile Manifesto to
understand why maximal flexibility is crucial in most real-world
application programming -- and therefore why, in said real world rather
than in the more academic circles Dr. Van Roy and Dr. Hadidi move in,
dynamic typing is generally preferable, and not such a tiny issue as
they make the difference to be.  Still, they at least show more
awareness of the issues, in devoting 3 excellent pages of discussion
about it, pros and cons, than almost any other book I've seen -- most
books have clearly delineated and preformed precedence one way or the
other, so the discussion is rarely as balanced as that;).


Alex