\DOC assoc
\TYPE {assoc : ''a -> (''a * 'b) list -> ''a * 'b}
\SYNOPSIS
Searches a list of pairs for a pair whose first component equals a
specified value.
\KEYWORDS
list.
\DESCRIBE
{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
{x}.
\FAILURE
Fails if no matching pair is found. This will always be the case if
the list is empty.
\EXAMPLE
{
- assoc 2 [(1,4),(3,2),(2,5),(2,6)];
> val it = (2, 5) : (int * int)
}
\SEEALSO
Lib.assoc1, Lib.assoc2, Lib.rev_assoc, Lib.find, Lib.mem, Lib.tryfind,
Lib.exists, Lib.all.
\ENDDOC