Arc

I have just read the Arc tutorial. Here are some comments.

Since functions of one argument are so often used in Lisp programs, Arc has a special notation for them. [... _ ...] is an abbreviation for (fn (_) (... _ ...)). So our first map example could have been written

arc> (map [+ _ 10] '(1 2 3))
(11 12 13 . nil)

I know this feature from Nemerle, and miss it when programming in other languages.

Another nice one seems to be ~ operator for negating a function, though would not be nearly as useful as the last one.

arc> (map ~odd '(1 2 3 4 5)) 
(nil t nil t nil)

Code for adding an element to a hashtable does not look very natural:

arc> (= (airports "Boston") 'bos)
bos

In Python it would be:

airports["Boston"] = 'bos