\DOC assoc1

\TYPE {assoc1 : ''a -> (''a * 'b) list -> (''a * 'b)option}

\SYNOPSIS
Searches a list of pairs for a pair whose first component equals a
specified value.

\KEYWORDS
list.

\DESCRIBE
{assoc1 x [(x1,y1),...,(xn,yn)]} returns {SOME (xi,yi)} for the first
pair {(xi,yi)} in the list such that {xi} equals {x}. Otherwise, {NONE}
is returned. The lookup is done on an eqtype, i.e., the SML
implementation must be able to decide equality for the type of {x}.

\FAILURE
Never fails.

\EXAMPLE
{
- assoc1 2 [(1,4),(3,2),(2,5),(2,6)];
> val it = SOME (2, 5) : (int * int)option
}


\SEEALSO
Lib.assoc, Lib.assoc2, Lib.rev_assoc, Lib.mem, Lib.tryfind, Lib.exists,
Lib.all.

\ENDDOC