What is a functional-style replacement for this loop?

Question

nums = [2 5 3 7]
result = []
result.push {x:nums[0]}
for n in nums.slice(1)
    result.push {n:n + result[-1].x}
log result
# [{x:2} {x:7} {x:10} {x:17}]

This is hard to express functionally using the function map because each element depends on the previous element. What is the correct functional solution for this algorithm?

Answer 1

simplest way i know avoids performance-robbing closures, variables, extra function overhead, and globals:

result= [2, 5, 3, 7].map(function(a){ return { x: this[0]+=a }; }, [0]);

JS provides the seldom-used 2nd .map() parameter to store any state you need between iterations.

It probably doesn't get any simpler than this, but don't know coffee, sorry...

EDIT: whipped up a dual-language (js+cs) demo: http://pagedemos.com/maptranforms/