assoc find the entry in an alist
for a given key, and return the
(key . value) pair.
assoc-ref do a similar
lookup, but return just the value.
Return the first entry in alist with the given key. The
return is the pair
(KEY . VALUE) from alist. If there’s
no matching entry the return is
assq compares keys with
equal?. See also SRFI-1
which has an extended
assoc (Association Lists).
Return the value from the first entry in alist with the given
#f if there’s no such entry.
assq-ref compares keys with
Notice these functions have the key argument last, like other
-ref functions, but this is opposite to what
etc above use.
When the return is
#f it can be either key not found, or
an entry which happens to have value
#f in the
assq etc above if you need to differentiate these cases.