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

Ken Tilton kentilton at gmail.com
Thu May 11 06:20:46 CEST 2006



Alex Martelli wrote:
> Stefan Nobis <snobis at gmx.de> wrote:
> 
> 
>>aleax at mac.com (Alex Martelli) writes:
>>
>>
>>>if anonymous functions are available, they're used in even more
>>>cases where naming would help
>>
>>Yes, you're right. But don't stop here. What about expressions? Many
>>people write very complex expression, that are hard to understand. A
>>good language should forbid these abuse and don't allow expressions
>>with more than 2 or maybe 3 operators!
> 
> 
> That would _complicate_ the language (by adding a rule).  I repeat what
> I've already stated repeatedly: a good criterion for deciding which good
> practices a language should enforce and which ones it should just
> facilitate is _language simplicity_.  If the enforcement is done by
> adding rules or constructs it's probably not worth it; if the
> "enforcements" is done by NOT adding extra constructs it's a double win
> (keep the language simpler AND push good practices).

Gosh, that looks like fancy footwork. But maybe I misunderstand, so I 
will just ask you to clarify.

In the case of (all syntax imaginary and not meant ot be Python):

      if whatever = 42
         dothis
         do that
         do something else
      else
         go ahead
         make my day

You do not have a problem with unnamed series of statements. But in the 
case of:

     treeTravers( myTree, lambda (node):
                              if xxx(node)
                                 print "wow"
                                 return 1
                              else
                                 print "yawn"
                                 return 0)

...no, no good, you want a named yawnOrWow function? And though they 
look similar, the justification above was that IF-ELSE was lucky enough 
to get multiline branches In the Beginning, so banning it now would be 
"adding a rule", whereas lambda did not get multiline In the Beginning, 
so allowing it would mean "adding a construct". So by positing "adding a 
rule or construct" as always bad (even if they enforce a good practice 
such as naming an IF branch they are bad since one is /adding/ to the 
language), the inconsistency becomes a consistency in that keeping IF 
powerful and denying lambda the same power each avoids a change?

In other words, we are no longer discussing whether unnamed multi-line 
statements are a problem. The question is, would adding them to lambda 
mean a change?

Oh, yeah, it would. :)

hth, kenny


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