Module Kw.Count

module Count: sig .. end

Counting Accumulators

Module for making accumulators that count

Example: consider this function that makes a set from a list of integers:

foldl (flip S.add) S.empty

Suppose we want to convert the function to also count the number of ints we've added; with the Count module we just need to change the function definition to:

foldl (Count.update (flip S.add)) (Count.init S.empty)

In other words, we just initialize our initial accumulator using Count.init, and then apply the Count.update combinator to our folding function.

Warning! Documentation bug: type t is actually abstract!

type 'a t = int * 'a

The type of counting accumulators

val init : ?i:int -> 'a -> int * 'a

init ?i a: convert initial accumulator value a to a counting accumulator

i : initial value for count

a : initial accumulator

val n : 'a * 'b -> 'a

n ca: extract count from counting accumulator ca

val acc : 'a * 'b -> 'b

acc ca: extract accumulator from counting accumulator ca

val pair : 'a -> 'a

pair ca: extract count and accumulator as a pair

val update : ?i:int -> ('a -> 'b -> 'c) -> int * 'a -> 'b -> int * 'c

update ?i f ca: return updated counting accumulator ca by applying f to ca and incrementing the count by i (default: 1)

val incr : ?i:int -> int * 'a -> int * 'a

incr ?i ca: return counting accumulator ca with count incremented by i (default: 1) but with accumulator unmodified

val withcount : ('a -> 'b) -> 'a * 'c -> 'c

withcount f ca: apply f to the count in ca (for side-effect, e.g. printing), returning the accumulator