defined : ('a, 'b) func -> 'a -> bool

SYNOPSIS
Tests if a finite partial function is defined on a certain domain value.

DESCRIPTION
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 defined f x returns true if the finite partial function f is defined on domain value x, and false otherwise.

FAILURE CONDITIONS
Never fails.

EXAMPLE
  # defined (1 |=> 2) 1;;
  val it : bool = true

  # defined (1 |=> 2) 2;;
  val it : bool = false

  # defined undefined 1;;
  val it : bool = false

SEE ALSO
|->, |=>, apply, applyd, choose, combine, defined, dom, foldl, foldr, graph, is_undefined, mapf, ran, tryapplyd, undefined.