annotate ppc/util.ml @ 0:bfdcc3820b32

Basis
author Mike Spivey <mike@cs.ox.ac.uk>
date Thu, 05 Oct 2017 08:04:15 +0100
parents
children
rev   line source
mike@0 1 (* ppc/util.ml *)
mike@0 2 (* Copyright (c) 2017 J. M. Spivey *)
mike@0 3
mike@0 4 (* |copy n x = [x; x; ...; x]| with |n| copies of |x| *)
mike@0 5 let rec copy n x = if n <= 0 then [] else x :: copy (n-1) x
mike@0 6
mike@0 7 (* |take n [x1; x2; ...] = [x1; x2; ...; xn]| *)
mike@0 8 let rec take n =
mike@0 9 function
mike@0 10 [] -> []
mike@0 11 | x::xs -> if n = 0 then [] else x :: take (n-1) xs
mike@0 12
mike@0 13 (* |drop n [x1; x2; ...] = [x_{n+1}; x_{n+2}; ...]| *)
mike@0 14 let rec drop n =
mike@0 15 function
mike@0 16 [] -> []
mike@0 17 | x::xs -> if n = 0 then x::xs else drop (n-1) xs
mike@0 18
mike@0 19 (* |can f x| is true if |f x| doesn't raise |Not_found| *)
mike@0 20 let can f x = try f x; true with Not_found -> false
mike@0 21
mike@0 22 (* |make_hash n [(x1, y1); ...]| creates a hash table of size |n|
mike@0 23 that initially contains the pairs |(x1, y1)|, ... *)
mike@0 24 let make_hash n ps =
mike@0 25 let table = Hashtbl.create n in
mike@0 26 List.iter (function (x, y) -> Hashtbl.add table x y) ps;
mike@0 27 table
mike@0 28
mike@0 29 (* |accum f [x1; x2; ...; xn] a| computes f xn (... (f x2 (f x1 a)) ...) *)
mike@0 30 let rec accum f ys a =
mike@0 31 match ys with
mike@0 32 [] -> a
mike@0 33 | x::xs -> accum f xs (f x a)