在CoffeeScript中的缺点（:)？

Question

Haskell provides the : function to prepend an item to a list:

*Main> :t (:)
(:) :: a -> [a] -> [a]

Example:

*Main> 1 : 2 : 3 : []
[1,2,3]

Does such a function/operator exist for CoffeeScript?

Answer 1

As far as I can tell, CoffeeScript does not implement Haskell-like lists. The closest method/function is the Array unshift method

However, the Haskell cons function creates a new list while preserving the original list, whereas Array.unshift modifies an existing array, so they really aren't the same thing.

There are a number implementations of linked-lists in CoffeeScript, eg:

• example 1
• example 2

but I don't see anything natively supported by CoffeeScript.

Answer 2

I'd second the native unshift method – although it will return the length of the resulting array, not the array itself , so you can't chain calls, like your example suggests.

As a fun alternative, CoffeeScript's ranges feature allows splicing , which could be used to prepend a value to an existing array:

array = [ 1, 2, 3 ]

array[..0] = [ 4, array[0] ]

console.log array # [ 4, 1, 2, 3 ]

More precisely, it removes the first element of the array and adds the two elements on the right-hand side of the assignment (your desired prependand and the original 0-value).

We can even chain it, by wrapping it in parentheses and bringing in the array's referencing variable:

array = [ 1, 2, 3 ]

(( array[..0] = [ 4, array[0] ] ) and array).unshift(5)

console.log array # [ 5, 4, 1, 2, 3 ]