Searches a list of pairs for a pair whose second component equals a specified
value.
DESCRIBE
An invocation rev_assoc y [(x1,y1),...,(xn,yn)] returns
the first (xi,yi) in the list such that yi equals y. The lookup is
done on an eqtype, i.e., the SML implementation must be able to decide
equality for the type of y.
FAILURE
Fails if no matching pair is found. This will always be the case if the
list is empty.
EXAMPLE
- rev_assoc 2 [(1,4),(3,2),(2,5),(2,6)];
> val it = (3, 2) : (int * int)