A running list of features from Python and Ruby and others that I'd like to see in either one, or a hybrid. Suggestions welcome.

languagefeatures.txt

From Python
-------------------------------------------
List comprehensions (and set/dictionary comprehensions too)
Decorators*
Implicit truthiness for values and containers (False: empty string, empty list, None, etc.)
Formatting w/o need to count braces or parens (much)
English keywords for logic operators (or, and, not, is)
Friendlier ternary syntax. (return x if x else y)

From Ruby
-------------------------------------------
Blocks
Optional parens on function calls
Pretzel shorthand (&:)
first/last on array
Symbols (ex: :foo)
Expression-based functions (no return)
Interrogative notation for methods (ex: #empty?) (These don't require boolean in Ruby, but would work better if they did.)
Base10-friendly formatting (1_000_000, etc.)   (Is this Ruby core or something from Active Support?)

C#
-------------------------------------------
Super-clean lambda syntax x => x*x
Simple properties


Erlang (and Clojure, others)
-------------------------------------------
Pattern matching to unpack data like [H|T] = SomeList  
Guards

Haskell
-------------------------------------------
type classes

Misc
-------------------------------------------
typedefs / type synonyms


Notes
-------------------------------------------
*For a language to work well there must be genuine synergy between the components. 
I wouldn't bring in any feature unless it fulfilled a clear need. 
For example, decorators are something that sprung up out of the constraints
of Python. It might make more sense to go with full-out macros or more granualar 
pre/post filters. It really depends on how the other features fit together.


Misc Ideas
-------------------------------------------
[Default Return Values]
As a companion to guards, it might be nice to have default return values for functions.
A function/method signature might look like this:

    def find_apples(criteria) or []

Where the 'or []' indicates the default value if no return value is specified. In this
case we're riffing on a common idiom in scripting languages of setting a default value
if we didn't get one back. Might as well do that in the function itself.

JSON/YAML friendly data structure notation. For instance in Ruby the hashrockets get in the way of having a common hash notation.


Guiding principles (spitballing here)
-------------------------------------------
No nulls (billion-dollar mistake)
Tail-call optimization