A critic of Guido's blog on Python's lambda

Chris Uppal chris.uppal at metagnostic.REMOVE-THIS.org
Wed May 10 10:18:18 CEST 2006


Petr Prikryl wrote:

>         for element in aCollection:
>             if element > 0:
>                 return True
>         return False

[I'm not sure whether this is supposed to be an example of some specific
language (Python ?) or just a generic illustration.  I'll take it as the
latter, since it makes my point easier to express.  I'll also exaggerate, just
a little...]

But now, in order to hack around the absence of a sensible and useful
feature -- /only/ in order to do so -- you have added two horrible new
complications to your language.  You have introduced a special syntax to
express conditionals, and (worse!) a special syntax to express looping.  Not
only does that add a huge burden of complexity to the syntax, and semantics, of
the language (and, to a lesser extent, its implementation), but it also throws
out any semblance of uniformity.

Once you've started down that route then you've lost all hope of user-defined
control structures which operate on a par with the built-in ones.  And please
note that "control structures" are not limited to C-style "for" "while" etc.

E.g. in Java there's an unresolved, and irresolvable, tension between whether a
failing operation should return an error condition or throw an exception -- the
problem is that exceptions are (IMO and most other peoples' here) intended for
exceptional conditions, and for many operations "failure" is not exceptional.
One, highly effective, resolution to the problem is for the operation to be
parameterised with the action to take if it fails (defaulting to code to raise
an exception).  In Java that approach, though technically possible, is totally
infeasible due to the pathetic overuse of unwanted syntax, and the underuse of
simple and powerful primitives.

E.g. can you add three-way comparisons (less-than, same-as, greater-than to,
say, Python with corresponding three-way conditional control structures to
supplement "if" etc ?  Are they on a semantic and syntactic par with the
existing ones ?  In Smalltalk that is trivial (too trivial to be particularly
interesting, even), and I presume the same must be true of Lisp (though I
suspect you might be forced to use macros).

I should say that if your example /is/ in fact Python, then I believe that
language allows fairly deep hooks into the execution mechanism, so that at
least the "for" bit can be mediated by the collection itself -- which is better
than nothing, but nowhere near what I would call "good".

    -- chris





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