(access coll key)
  coll: any type
  key: any type
  returns any type

Retrieves an item from a collection.

The ? special syntax can be used to perform fallible indexing: [coll (? key)]. In that case, if the index key is not present, the function succeeds and returns #n.

When coll is a deque, slicing syntax is supported: [deq i : j], where either i or j may be absent. This returns a newly-allocated, mutable deque which contains all of the elements from i inclusive to j exclusive. Negative indexes are supported.

When key is an iterator, this function returns a new iterator which produces [coll item] for each item produced by key.

(access coll key) is usually abbreviated as [coll key].