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 dot_index = index s '.' in

    let lhs = sub s 0 dot_index in
    let rhs = sub s (idx + 1) (len - idx - 1) in

    let numerator = concat "" [lhs;rhs] in

    let denominator = power_num (num_of_int 10) (length rhs) in

    let n = num_of_string (concat "" [numerator; "\"; denominator]) 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