Hi list,

Here is my speculative language idea for Python:

Allow the following alternative spelling of the keyword `lambda':

λ

(That is "Unicode Character 'GREEK SMALL LETTER LAMDA' (U+03BB).")

Background:

I have been using the Vim "conceal" functionality with a rule which visually

replaces lambda with λ when editing Python files. I find this a great improvement in

readability since λ is visually less distracting while still quite distinctive.

(The fact that λ is syntax-colored as a keyword also helps with this.)

However, at the moment the nice syntax is lost when looking at the file through another editor or viewer.

Therefore I would really like this to be an official part of the Python syntax.

I know people have been clamoring for shorter lambda-syntax in the past, I think this is

a nice minimal extension.

Example code:

  lst.sort(key=lambda x: x.lookup_first_name())

  lst.sort(key=λ x: x.lookup_first_name())

  # Church numerals

  zero = λ f: λ x: x

  one = λ f: λ x: f(x)

  two = λ f: λ x: f(f(x))

(Yes, Python is my favorite Scheme dialect. Why did you ask?)

Note that a number of other languages already allow this. (Racket, Haskell).

You can judge the aesthetics of this on your own code with the following sed command.

  sed 's/\<lambda\>/λ/g'

Advantages:

* The lambda keyword is quite long and distracts from the "meat" of the lambda expression. 

  Replacing it by a single-character keyword improves readability.

* The resulting code resembles more closely mathematical notation (in particular, lambda-calculus notation),

  so it brings Python closer to being "executable pseudo-code".

* The alternative spelling λ/lambda is quite intuitive (at least to anybody who knows Greek letters.)

Disadvantages:

For your convenience already noticed here:

* Introducing λ is introducing TIMTOWTDI.

* Hard to type with certain editors.

  But note that the old syntax is still available.

  Easy to fix by upgrading to VIM ;-) 

* Will turn a pre-existing legal identifier λ into a keyword.

  So backward-incompatible.

Needless to say, my personal opinion is that the advantages outweigh the disadvantages. ;-)

Greetings,

Stephan