Task 3 from West London Hack Night Feb 26 2014

wlhn-20140226-task3.elm

-- DOES NOT COMPILE

import String (toInt, toList)

data Node = Op String Node Node | Value Int

listToInt l = case toInt (join "" l) of
    Just x -> x

tokeniseOp hd tl tokenAccum partialAccum =
    if length partialAccum > 0 then
        tokenise tl (tokenAccum ++ (listToInt partialAccum) ++ hd) partialAccum
    else
        tokenise tl (tokenAccum ++ hd) partialAccum

tokenise l tokenAccum partialAccum = case l of
    hd :: tl ->
        case hd of
            "+" -> tokeniseOp hd tl tokenAccum partialAccum
            "-" -> tokeniseOp hd tl tokenAccum partialAccum
            "*" -> tokeniseOp hd tl tokenAccum partialAccum
            "/" -> tokeniseOp hd tl tokenAccum partialAccum
            _ -> tokenise tl tokenAccum (partialAccum ++ hd)
    [] -> tokenAccum -- handle partialAccum here

parse s = tokenise (toList s) [] []

-- test = "34+22*5"

-- assert (parse text) == ((Op "+") (Int 34) ((Op "*") (Int 22) (Int 5)))