[Python-ideas] [Wild Idea] Static Ducks

Stephen J. Turnbull stephen at xemacs.org
Fri Sep 25 06:44:00 CEST 2009

Mike Meyer writes:
 > On Thu, 24 Sep 2009 20:06:22 -0400
 > Gerald Britton <gerald.britton at gmail.com> wrote:
 > > I think that the idea that there is a continuum from weak typing to
 > > strong typing is useful.
 > I think it's fundamentally broken, at least as badly as the notion of
 > a political spectrum from liberal to conservative. The problem with
 > both of those is that there's more than one axis involved.

The notion that you can't order multidimensional sets (where each
dimension is ordered) is simply wrong.  You do it every day when you
decide to have "a Big Mac with coffee" instead of "a QuarterPounder
with a vanilla shake".

It is always possible to approximately reduce a multidimensional set
to a one-dimensional "spectrum" by use of a mechanical procedure
called principal components analysis (the "direction" of the spectrum
is the principal eigenvector, in fact).  This procedure provides
measures of the quality of the approximation as well (eg, the ratio of
the principal eigenvalue to the second eigenvalue).

The question here then is simply "what is the quality of the
approximation, and are there structural shifts to account for?"

 > Just as people can have a liberal position on one issue while
 > having a conservative position on another, languages can have some
 > features that give them "weak typing" and others that give them
 > "strong typing".

They can take such positions, but historically the correlations were
generally high.  What has happened in politics in many countries is
that there has been a structural realignment such that the component
axis traditionally labeled "liberal to conservative" is no longer so
much stronger than other components of variation.  That doesn't mean
that the traditional axis was never useful, nor that a new principal
axis hasn't been established (although I don't think it has been
established yet in American politics).

 > Axis so far: declarations: yes/no/optional. Variables have types:
 > (yes/no/optional). Implicit conversion: yes/no, with a different
 > answer possible for every operand and tuple of operators types in the
 > language.

My personal resolution of strong vs. weak typing is that it's useful
to help explain which languages I like (strongly typed ones) vs. those
I don't.  In this, only the implicit conversion axis matters much.
Whether variables have types, or declarations are needed, are
implementation details related to when type checking takes place (and
thus compile-time vs. runtime efficiency), and the tradeoff between
translator complexity and burden on the developer to specify things.
There are also issues of discoverability and readability which may
make it desirable to be somewhat explicit even though a high degree of
translator complexity is acceptable to me.

 > > It's probably possible to devise some sort of metric to be able to
 > > place a given language on the weak-strong scale.
 > I don't think it's possible, because your scale is really a space.

It's always possible.  Proving that is why Georg Cantor is so famous.
The question is whether it's compatible with "what people think", and
the answer is "if you must cover all corner cases, no" (ditto, Kenneth
Arrow).  Can you achieve something usable?  I don't know, which is why
I'd like to see Mathias's professor's slide!

 > > Where would Python fall?  Probably towards the weak end.  Is that
 > > bad?  No way!
 > Like I said, it's usually considered to be near the strong end,
 > because it does few implicit conversion.


Furthermore, Python's builtin implicit conversions (with the exception
of the nearly universal conversion to Boolean, which is a special case
anyway) are mostly natural embeddings.  Even in cases like
"range(10.0)" Python refuses to guess.

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