[Python-Dev] Let's send lambda to the shearing shed (Re: Let's just *keep* lambda)

Bengt Richter bokr at oz.net
Thu Feb 9 21:53:39 CET 2006

On Thu, 09 Feb 2006 16:41:10 +1300, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

>My thought on lambda at the moment is that it's too VERBOSE.
>If a syntax for anonymous functions is to pull its weight,
>it needs to be *very* concise. The only time I ever consider
>writing a function definition in-line is when the body is
>extremely short, otherwise it's clearer to use a def instead.
>Given that, I do *not* have the space to waste with 6 or 7
>characters of geeky noise-word.
OTOH, it does stand out as a flag to indicate what is being done.

>So my vote for Py3k is to either
>1) Replace lambda args: value with
>   args -> value
>or something equivalently concise, or
Yet another bike shed color chip:

    !(args:expr)   # <==> lambda args:expr
    !(args::suite) # <==> (lambda args::suite)

(where the latter lambda form requires outer enclosing parens) But either "::" form
allows full def suite, with indentation for multilines having left edge of single indent
defined by first line following the "::"-containing line, and explicit returns for values
required and top suite ending on closing outer paren)

Probable uses for the "::" form would be for short inline suite definitions
    !(x::print x)               # <==> (lambda x::print x) & etc. similarly
    !(::global_counter+=1;return global_counter)
    !(::raise StopIteration)()  # more honest than iter([]).next()

but the flexibility would be there for an in-context definition, e.g.,

    sorted(seq, key= !(x::
        try: return abs(x)
        except TypeError: return 0))

and closures could be spelled

    !(c0,c1:!(x:c0+c1*x))(3,5)   # single use with constants is silly spelling of !(x:3+5*x)

Hm, are the latter two really better for eliminating "lambda"? Cf:

    sorted(seq, key=(lambda x::
        try:return abs(x)
        except TypeError: return 0))
    (lambda c1,c2:lambda x:c0+c1*x)(3,5) # also silly with constants

I'm not sure. I think I kind of like lambda args:expr and (lambda args::suite)
but sometimes super-concise is nice ;-)

>2) Remove lambda entirely.

Bengt Richter

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