parse_dec.ml

(*
 * Parsing a decimal into an arbitrary precision number in Ocaml.
 *
 * Input not checked as the parser will sanitise the input.
 *
 * ocamlfind ocamlc -package num -linkpkg -o parse_dec parse_dec.ml
 *)
open Num
open String

let num_of_dec_string s =
    let idx = index s '.' in
    let len = length s in
    let whole = sub s 0 idx in
    let frac = sub s (idx + 1) (len - idx - 1) in
    let scale = power_num (num_of_int 10) (num_of_int (length frac)) in
    let conc = concat "" [whole; frac] in
    let move_dp = num_of_string conc in
    let n = div_num move_dp scale in
    Printf.printf "%s.%s=%s\n" whole frac (string_of_num n);;

while true do
    let line = read_line () in
    num_of_dec_string line
done