An accumulator

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OCaml programs

An accumulator

Consider the following codes (** Summation of all the integers in a list *) (* *) let rec sum_int_list = function lx -> if is_empty_list (lx) then 0 else (function x, y -> x + y) (head (lx), sum_int_list (tail (lx))) (** Product of all the reals in a list *) (* *) let rec prod_float_list = function lx -> if is_empty_list (lx) then 1. else (function x, y -> x *. y) (head (lx), prod_float_list (tail (lx))) (** Logical conjunction of all the booleans in a list *) (* *) let rec and_list = function lx -> if is_empty_list (lx) then true else (function x, y -> x & y) (head (lx), and_list (tail (lx)))

Look at the definitions of  sum_int_list ,  prod_float_list  and  and_list . Clearly their structures are similar. Transform what is identical in them into a functional value (named  accumul_right ) that can be applied to obtain the values of  sum_int_list , of  prod_float_list  and of  and_list  :  let accumul_right = function (op, neutral) -> (let rec f = function lx -> if is_empty_list (lx) then neutral else op (head (lx), f (tail (lx))) in f)

The type of  accumul_right  is ('a * 'b -> 'b) * 'b -> ('a list -> 'b)

An example of application of the higher-order function  accumul_right : (** Logical disjunction of all the booleans in a list *) (* *) accumul_right ((function x, y -> x or y), false) Now an example of application of the result of this application of the higher-order function  accumul_right : (** Computes the list of three times each element in a list of integers *) (* *) (accumul_right ((function x, y -> x or y), false)) ([2 + 2 = 5 ; 6 - 3 = 9])

An accumulator

Documentation and user's manual

Table of contents

OCaml programs