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

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

and !(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))

and (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. -1

Regards, Bengt Richter

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