`map` applies a function to elements of one or more sequentially iterable collections. With collections supplied, it returns a lazy sequence of results—not a key-value map. Prefer a function without side effects: laziness does not guarantee that it will be called exactly once per element. section 3.5.2
Its contract depends on how many collections follow the function:
- `(map f coll)` calls `f` with one element at a time and returns a lazy sequence. section 3.5.2
- `(map f c1 c2 & colls)` calls `f` with corresponding elements from each collection. `f` must accept that many arguments; results stop at the shortest collection. section 3.5.2
- `(map f)` returns a transducer instead of processing a collection immediately. section 3.5.2 section 7.2
Transform one collection
`(map - (range 10))` returns `(0 -1 -2 -3 -4 -5 -6 -7 -8 -9)`. section 3.5.2
Combine corresponding elements
`(map str (range 10) ["a" "b" "c"] "hijklm")` returns `("0ah" "1bi" "2cj")`. The three-element vector ends the mapping. section 3.5.2
When the function also needs each element’s position, use `map-indexed`. For example, `(into {} (map-indexed vector [:a :b :c]))` yields `{0 :a, 1 :b, 2 :c}`. section 3.5.2
