Levenshtein distance algorithm in CoffeeScript

levenshtein.coffee

###
# @desc: Recursive Implementation of Levenshtein distance algorithm
# according to Wikipedia's pseudocode implementation of it
# @author: Asdrúbal Suárez (Twitter @asdrubalivan)
###
levenshteinInternal = (s, len_s, t, len_t) ->
    if len_s is 0
        return len_t
    if len_t is 0
        return len_s
    cost = if s[len_s - 1] is t[len_t - 1] then 0 else 1
    l1 = levenshteinInternal(s, len_s - 1, t, len_t) + 1
    l2 = levenshteinInternal(s, len_s, t, len_t - 1) + 1
    l3 = levenshteinInternal(s, len_s - 1, t, len_t - 1) + cost
    Math.min l1, l2, l3

levenshtein = (s, t) ->
    levenshteinInternal s, s.length, t, t.length

console.log levenshtein("book", "back")