Searches a list of pairs for a pair whose second component equals a specified
value.
DESCRIPTION
An invocation rev_assoc y [(x1,y1),...,(xn,yn)] locates
the first (xi,yi) in a left-to-right scan of the list such that
yi equals y. Then xi is returned. 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 : int