foldr : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) func -> 'c -> 'c

SYNOPSIS

Folds an operation iteratively over the graph of a finite partial function.

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. If a finite partial function p has graph [x1,y1; ...; xn,yn] then the application foldl f p a returns

 f x1 y1 (f x2 y2 (f x3 y3 (f ... (f xn yn a) ... )))

Note that the order in which the pairs are operated on depends on the internal structure of the finite partial function, and is often not the most obvious.

FAILURE CONDITIONS

Fails if one of the embedded function applications does.

EXAMPLE

  # let f = (1 |-> 2) (2 |=> 3);;
  val f : (int, int) func = 

  # graph f;;
  val it : (int * int) list = [(1, 2); (2, 3)]

  # foldr (fun x y a -> (x,y)::a) f [];;
  val it : (int * int) list = [(2, 3); (1, 2)]

Note how the pairs are actually processed in the opposite order to the order in which they are presented by graph. The order will in general not be obvious, and generally this is applied to operations with appropriate commutativity properties.