\DOC |=>

\TYPE {(|=>) : 'a -> 'b -> ('a, 'b) func}

\SYNOPSIS
Gives a one-point finite partial function.

\DESCRIBE
This is one of a suite of operations on finite partial functions, type
{('a,'b)func}. These may sometimes be preferable to ordinary functions since
they permit more operations such as equality comparison, extraction of domain
etc. The call {x |=> y} gives a finite partial function that maps {x} to {y}
and is undefined for all arguments other than {x}.

\EXAMPLE
{
  # let f = (1 |=> 2);;
  val f : (int, int) func = <func>

  # apply f 1;;
  val it : int = 2

  # apply f 2;;
  Exception: Failure "apply".
}

\SEEALSO
|->, apply, applyd, choose, combine, defined, dom, foldl, foldr,
graph, is_undefined, mapf, ran, tryapplyd, undefine, undefined.

\ENDDOC