PolishCalculator

#load "str.cma";;
module PolishCalculator =
	struct
		type expr= {num:int; op:string}
		
	(*this function recognize +,-,*,/,** *)
		let evaluatelist x list=
			let evaluate x expr= match expr with
			| {num; op="+"} -> x+num
			| {num; op="*"} -> x*num
			| {num; op="**"} -> int_of_float(float_of_int x**float_of_int num)
			| {num; op="/"} -> x/num	
			| {num; op="-"} -> x-num			
			| _ -> raise (Invalid_argument "Unknown operator or missing argument.")
			in
			let rec eval x = function
				| [] -> x
				| h::tl -> eval (evaluate x h) tl 
			in
			eval x list


				
	(*from string to exprlist*)
		let fste string=
			let stringlist = Str.split (Str.regexp "[ \t]+") string			
			and
		  	cexp h s= {num=int_of_string h;op= s} 
			in			
			let rec listofexp acc = function
				| [] -> acc
				| h::s::tl -> listofexp ((cexp h s)::acc) tl
				| _::[] -> acc
			in
			List.rev (listofexp [] stringlist) 
	end 
	
	(*this function take a first number to calculate on and a string on format "3 + 4 / 5 * 6 +", with spaces between char*)
	let calculate firstnum str = PolishCalculator.evaluatelist firstnum (PolishCalculator.fste str)