simple calc parser

calc.fs

#if INTERACTIVE
#I @"/Users/kevin/Projects/FSParsec/packages/FParsec.1.0.1/lib/net40-client/"
#r @"FParsecCS.dll"
#r @"FParsec.dll"
#endif

open FParsec

type Expr = Op of string * Expr * Expr | Num of float

let ws  = spaces
let isSymbolicOperatorChar = isAnyOf "*+-^/"
let remainingOpChars_ws = manySatisfy isSymbolicOperatorChar .>> ws

let opp = new OperatorPrecedenceParser<Expr, string, unit>()
let expr = opp.ExpressionParser
opp.TermParser <- (pfloat .>> ws |>> Num) <|> between (ws >>.pstring "(" .>> ws) (ws >>.pstring ")" .>> ws) expr

let addSymbolicInfixOperators (prefix, precedence) =
    let op = InfixOperator(prefix, remainingOpChars_ws,
                           precedence, Associativity.Left, (),
                           fun remOpChars expr1 expr2 ->
                               Op(prefix + remOpChars, expr1, expr2))
    opp.AddOperator(op)

seq [("^",30); ("*",20); ("/", 20); ("+",10); ("-", 10)] |> Seq.iter addSymbolicInfixOperators

let calc str = 
    let rec calc'= 
        function
        | Num x->x
        | Op (op,a,b) -> 
            let func = match op with | "+" ->  (+) | "-" -> (-) | "*" -> (*) | "/" -> (/) | "^" -> ( ** ) | _ -> failwith ("Unknown operator "+ op)
            func (calc' a) (calc' b)
    match run opp.ExpressionParser str with
    | Success (a,_,_) -> calc' a
    | Failure(errorMsg, _, _) -> failwith ("Failure: " + errorMsg)
     
//calc "2^16"
calc "1+2*(2  +3)/3"
calc " (1 +2+3)/6 "
calc "(1*2+3)/6"
calc "(1+2*3-1)/6"