\DOC assoc
\TYPE {assoc : ''a -> (''a * 'b) list -> ''a * 'b}
Searches a list of pairs for a pair whose first component equals a
specified value.
{assoc x [(x1,y1),...,(xn,yn)]} returns the first {(xi,yi)} in the
list such that {xi} equals {x}. The lookup is done on an eqtype, i.e.,
the SML implementation must be able to decide equality for the type of
Fails if no matching pair is found. This will always be the case if
the list is empty.
- assoc 2 [(1,4),(3,2),(2,5),(2,6)];
> val it = (2, 5) : (int * int)
Lib.assoc1, Lib.assoc2, Lib.rev_assoc, Lib.find, Lib.mem, Lib.tryfind,
Lib.exists, Lib.all.