(indexed-sources sources)
Take a seq of source file names and return a map from
file number to integer index.
Source
(defn indexed-sources
"Take a seq of source file names and return a map from
file number to integer index."
[sources]
(->> sources
(map-indexed (fn [a b] [a b]))
(reduce (fn [m [i v]] (assoc m v i)) {})))