Comprehension Patterns for Coffeescript

comprehensionsPatterns.coffee

#map equivalent
x = for i in ['a', 'b', 'c']
  i + i
#=> ['aa', 'bb', 'cc']

#for each equivalent
for i in ['a', 'b', 'c']
  #do side effect
  null

#inject/collect equivalent example
for own key, val of [1, 2, 3, 4]
  memo = (memo || 0) + val
  
#inject/collect equivalent general form
for own, key, val of someObjOrArray
  memo = (memo || initVal) #set some intial value
  memo = fn(memo, key, val)  #operate on previous memo to get current memo