Why don't people like lisp?

[Alex Martelli]

Paul Rubin wrote:
   ...
> This is untested but looks simpler than the lisp example:
> 
>     def mostn (fn, lst):
>       max = None
>       for a in lst:
>          score = fn(lst)

Perhaps "score = fn(a)" ?

>          if max is None or score > max:
>             max = score
>             ret = [a]
>          elif score == max:
>             ret.append(a)
>       return ret

it it all right to raise an exception if lst is empty?
I'm not sure of the lisp example's behavior in that case,
but I suspect it returns an empty list and None.  In
that case, we may need to initialize ret to [] too.

Stylistically (but it's just me) I don't much like that
"first-time switch" use -- null in lisp, None in Python.
An alternative might be to treat the empty lst as
an exceptional case:

def mostfn(fn, lst):
    try: a = lst[0]
    except IndexError: return [], None
    ret, max = [], fn(a)
    for a in lst:
        score = fn(a)
        if score > max:
            max = score
            ret = [a]
        elif score == max:
            ret.append(a)
    return ret, max

a _bit_ more complicated than Paul's code, and calls
fn twice on lst[0], but it caters to my dislike for 
"first-time switches"...;-).  One could remove the
double-call problem by changing the start to:

def mostfn(fn, lst):
    it = iter(lst)
    try: a = it,next()
    except StopIteration: return [], None
    ret, max = [a], fn(a)
    for a in it:
        ...

If taking O(N) auxiliary memory was acceptable, of 
course, there would be an alternate possibility:

def mostfn(fn, lst):
    if not lst: return [], None
    aux = [ (fn(a), a) for a in lst ]
    Max = max([ f for f, a in aux ])
    return [ a for f, a in aux if f==Max ], Max

Typical problem with all high-level languages --
they often make most attractive an approach that
may not be quite as spare of bytes and cycles as 
some lower-level one!-)  [A simple test with
fn=lambda x:x%333 and lst=range(9999) shows the
lower-level approach is over 3 times faster,
both with and without psyco.proxy on both].


Alex